Comparative Descriptions

The Engineer's Sketch-Book	A Pattern Language
An example of the manner in which the book should be used will now be given. It will serve to indicate in a practical way the method to be pursued by a reader in order to select from its Sections the various details required to build up a given piece of mechanism. Suppose it is required to design a reciprocating carriage or frame. In the first place the designer should reduce his problem to its elements-nature of the material to be treated (assuming that the frame is for sieving or segregation of a material), output required, speed, size, method of drive, suitability to surrounding conditions, etc. Having done this, the following points will come up for consideration. Is the drive to be direct, from motor or shaft, or indirect, through chain, gear, rope or belt? If the former, a reference to Clutches, Section 15, pages 46 to 49, and to Couplings, Section 16, pages 48 to 51, will be helpful. If the latter, Friction Gear, Section 38, pages 118 to 121, Rope Gear, Section 66, pages 212 to 214, Belt Gear, Section 3, pages 8 to 11, and Toothed Gear, Section 84, pages 276 to 283, may be consulted. Section 40, pages 126 to 133, showing Various Devices in Gearing, may be looked up, as a solution of some special problem in transmission may possibly be found applicable to the case under consideration. The next question is the design of a satisfactory reciprocating movement, having regard to the conditions-material to be treated (i.e. heavy or light, fine or gross, adhesive or not, etc.) or other duty, rate of output, etc. Section 21, pages 68 to 75, gives diagrams of practically every device utilisable for the conversion of Circular into Reciprocating Motion. If an intermittent movement is required, Section 62, pages 202 to 209, will provide the solution. At this point Section 72, pages 226 to 229, dealing with Screening, may offer some useful information. The carriage or frame will require support according to the circumstances (speed, kind of vibratory movement, accessibility etc.), and an inspection of Section 46, pages 142 to 149, showing Bearings, or Section 48, pages 152 to 159 showing Link Suspension devices, may be made. On the other hand, if a sliding support or guide is preferred, Section 39, pages 120 to 127, should be consulted. A mechanism equipped with a Variable Speed device, either for driving the carriage or for feeding it, may possibly be of service. In this case, Section 88, pages 286 to 295, will be found to disclose the elements of every practical means of attaining this end. Reciprocating bodies, especially if they are heavy, call for means of checking their motion at the end of their travel. This may be effected by a braking device or by a cam or similar gear. Information on Brakes and Retarding appliances will be found in Section 5, pages 12 to 17, and on Cams, Tappets and Wipers in Section 9, pages 26 to 31. Section 29, on Cushioning, may provide some ideas on this subject, see pages 96 and 97. Lubrication is a subject that is often neglected, nevertheless it is often the most vital and consequently the most vulnerable part of an appliance called on to perform severe duty. Forced or mechanically operated lubrication is now generally recognised as an essential of the design of continuously operating mechanisms. In Section 51, pages 174 to 177, will be found indications of the various methods of attacking this problem. This example, in which the possible references are by no means exhausted, will demonstrate-it is hoped-that an intelligent and diligent use of this book will provide the searcher with very wide and thoroughly practical assistance, bearing on every aspect of the design he has to produce.	CHOOSING A LANGUAGE FOR YOUR PROJECT All 253 patterns together form a language. They create a coherent picture of an entire region, with the power to generate such regions in a million forms, with infinite variety in all the details. It is also true that any small sequence of patterns from this language is itself a language for a smaller part of the environment; and this small list of patterns is then capable of generating a million parks, paths, houses, workshops, or gardens. For example, consider the following ten patterns: PRIVATE TERRACE ON THE STREET (140) SUNNY PLACE (161) OUTDOOR ROOM (163) SIX-FOOT BALCONY (167) PATHS AND GOALS (120) CEILING HEIGHT VARIETY (190) COLUMNS AT THE CORNERS (212) FRONT DOOR BENCH (242) RAISED FLOWERS (245) DIFFERENT CHAIRS (251) This short list of patterns is itself a language: it is one of a thousand possible languages for a porch, at the front of a house. One of us chose this small language, to build a porch onto the front of his house. This is the way the language, and its patterns, helped to generate the porch. I started with PRIVATE TERRACE ON THE STREET (140). That pattern calls for a terrace, slightly raised, connected to the house, and on the street side, SUNNY PLACE (161) suggests that a special place on the sunny side of the yard should be intensified and made into a place by the use of a patio, balcony, outdoor room, etc. I used these two patterns to locate a raised platform on the south side of the house. To make this platform into an OUTDOOR ROOM (163), I put it half uner the existing roof overhang, and kept a mature pyracanthus tree right smack in the middle of the platform. The overhead foliage of the tree added to the roof-like enclosure of the space. I put a wind screen of fixed glass on the west side of the platform too, to give it even more enclosure. I used SIX-FOOT BALCONY (167) to determine the size of the platform. But this pattern head to be used judiciously and not blindly-the reasoning for the pattern had to do with the minimum space required for people to sit comfortably and carry on a discussion around a small side-table. Since I wanted space for at least two of these conversation areas-one under the roof for very hot or rainy days, and one out under the sky for days when you wanted to be full in the sun, the balcony had to be made 12 x 12 feet square. Now PATHS AND GOALS (120): Usually this pattern deals with large paths in a neighbourhood, and comes much earlier in a language. But I used it in a special way. It says that the paths which naturally get formed by people's walking, on the land, should be preserved and intensified. Since the path to our front door cut right across the corner of the place where I had planned to put the platform, I cut the corner of the platform off. The height of the platform above the ground was determined by CEILING HEIGHT VARIETY (190). By building the platform approximately one foot above the ground line, the ceiling height of the covered portion came out at between 6 and 7 feet-just right for a space as small as this. Since this height above the ground level is just about right for sitting, the pattern FRONT DOOR BENCH (242) was automatically satisfied. There were three columns standing, supporting the roof over the old porch. They had to stay where they are, because they hold the roof up. But, following COLUMNS AT THE CORNERS (212), the platform was carefully tailored to their positions-so that the columns help define the social spaces on either side of them. Finally we put a couple of flower boxes next to the "front door bench"-it's nice to smell them when you sit there-according to RAISED FLOWERS (245). And the old chairs you can see in the porch are DIFFERENT CHAIRS (251).
Barber, T.W. The Engineer's Sketch-Book 7th Edition, New Impression, 1946 E. & F. N. Spon, London. pp xiii-xvi	Alexander, C., Ishikawa, S., Silverstein, M. et. al. A Pattern Language, 1977 Oxford University Press, New York. pp xxxv-xxxvii

The Engineer's Sketch-Book

A Pattern Language

An example of the manner in which the book should be used will now be given. It will serve to indicate in a practical way the method to be pursued by a reader in order to select from its Sections the various details required to build up a given piece of mechanism.

Suppose it is required to design a reciprocating carriage or frame.

In the first place the designer should reduce his problem to its elements-nature of the material to be treated (assuming that the frame is for sieving or segregation of a material), output required, speed, size, method of drive, suitability to surrounding conditions, etc. Having done this, the following points will come up for consideration. Is the drive to be direct, from motor or shaft, or indirect, through chain, gear, rope or belt? If the former, a reference to Clutches, Section 15, pages 46 to 49, and to Couplings, Section 16, pages 48 to 51, will be helpful. If the latter, Friction Gear, Section 38, pages 118 to 121, Rope Gear, Section 66, pages 212 to 214, Belt Gear, Section 3, pages 8 to 11, and Toothed Gear, Section 84, pages 276 to 283, may be consulted. Section 40, pages 126 to 133, showing Various Devices in Gearing, may be looked up, as a solution of some special problem in transmission may possibly be found applicable to the case under consideration.

The next question is the design of a satisfactory reciprocating movement, having regard to the conditions-material to be treated (i.e. heavy or light, fine or gross, adhesive or not, etc.) or other duty, rate of output, etc.

Section 21, pages 68 to 75, gives diagrams of practically every device utilisable for the conversion of Circular into Reciprocating Motion. If an intermittent movement is required, Section 62, pages 202 to 209, will provide the solution. At this point Section 72, pages 226 to 229, dealing with Screening, may offer some useful information. The carriage or frame will require support according to the circumstances (speed, kind of vibratory movement, accessibility etc.), and an inspection of Section 46, pages 142 to 149, showing Bearings, or Section 48, pages 152 to 159 showing Link Suspension devices, may be made. On the other hand, if a sliding support or guide is preferred, Section 39, pages 120 to 127, should be consulted.

A mechanism equipped with a Variable Speed device, either for driving the carriage or for feeding it, may possibly be of service. In this case, Section 88, pages 286 to 295, will be found to disclose the elements of every practical means of attaining this end.

Reciprocating bodies, especially if they are heavy, call for means of checking their motion at the end of their travel. This may be effected by a braking device or by a cam or similar gear. Information on Brakes and Retarding appliances will be found in Section 5, pages 12 to 17, and on Cams, Tappets and Wipers in Section 9, pages 26 to 31. Section 29, on Cushioning, may provide some ideas on this subject, see pages 96 and 97. Lubrication is a subject that is often neglected, nevertheless it is often the most vital and consequently the most vulnerable part of an appliance called on to perform severe duty. Forced or mechanically operated lubrication is now generally recognised as an essential of the design of continuously operating mechanisms. In Section 51, pages 174 to 177, will be found indications of the various methods of attacking this problem.

This example, in which the possible references are by no means exhausted, will demonstrate-it is hoped-that an intelligent and diligent use of this book will provide the searcher with very wide and thoroughly practical assistance, bearing on every aspect of the design he has to produce.

CHOOSING A LANGUAGE FOR YOUR PROJECT

All 253 patterns together form a language. They create a coherent picture of an entire region, with the power to generate such regions in a million forms, with infinite variety in all the details.

It is also true that any small sequence of patterns from this language is itself a language for a smaller part of the environment; and this small list of patterns is then capable of generating a million parks, paths, houses, workshops, or gardens.

For example, consider the following ten patterns:

PRIVATE TERRACE ON THE STREET (140)
SUNNY PLACE (161)
OUTDOOR ROOM (163)
SIX-FOOT BALCONY (167)
PATHS AND GOALS (120)
CEILING HEIGHT VARIETY (190)
COLUMNS AT THE CORNERS (212)
FRONT DOOR BENCH (242)
RAISED FLOWERS (245)
DIFFERENT CHAIRS (251)

This short list of patterns is itself a language: it is one of a thousand possible languages for a porch, at the front of a house. One of us chose this small language, to build a porch onto the front of his house. This is the way the language, and its patterns, helped to generate the porch.

I started with PRIVATE TERRACE ON THE STREET (140). That pattern calls for a terrace, slightly raised, connected to the house, and on the street side, SUNNY PLACE (161) suggests that a special place on the sunny side of the yard should be intensified and made into a place by the use of a patio, balcony, outdoor room, etc. I used these two patterns to locate a raised platform on the south side of the house.

To make this platform into an OUTDOOR ROOM (163), I put it half uner the existing roof overhang, and kept a mature pyracanthus tree right smack in the middle of the platform. The overhead foliage of the tree added to the roof-like enclosure of the space. I put a wind screen of fixed glass on the west side of the platform too, to give it even more enclosure. I used SIX-FOOT BALCONY (167) to determine the size of the platform. But this pattern head to be used judiciously and not blindly-the reasoning for the pattern had to do with the minimum space required for people to sit comfortably and carry on a discussion around a small side-table. Since I wanted space for at least two of these conversation areas-one under the roof for very hot or rainy days, and one out under the sky for days when you wanted to be full in the sun, the balcony had to be made 12 x 12 feet square.

Now PATHS AND GOALS (120): Usually this pattern deals with large paths in a neighbourhood, and comes much earlier in a language. But I used it in a special way. It says that the paths which naturally get formed by people's walking, on the land, should be preserved and intensified. Since the path to our front door cut right across the corner of the place where I had planned to put the platform, I cut the corner of the platform off. The height of the platform above the ground was determined by CEILING HEIGHT VARIETY (190). By building the platform approximately one foot above the ground line, the ceiling height of the covered portion came out at between 6 and 7 feet-just right for a space as small as this. Since this height above the ground level is just about right for sitting, the pattern FRONT DOOR BENCH (242) was automatically satisfied.

There were three columns standing, supporting the roof over the old porch. They had to stay where they are, because they hold the roof up. But, following COLUMNS AT THE CORNERS (212), the platform was carefully tailored to their positions-so that the columns help define the social spaces on either side of them.

Finally we put a couple of flower boxes next to the "front door bench"-it's nice to smell them when you sit there-according to RAISED FLOWERS (245). And the old chairs you can see in the porch are DIFFERENT CHAIRS (251).

Barber, T.W. The Engineer's Sketch-Book 7th Edition, New Impression, 1946 E. & F. N. Spon, London.
pp xiii-xvi

Alexander, C., Ishikawa, S., Silverstein, M. et. al. A Pattern Language, 1977 Oxford University Press, New York.
pp xxxv-xxxvii