PREFACE.

The study of Graphic Statics, as a subject sui generis , has made but little progress inEngland, though the great value of numerous Graphic methods has long been fullyacknowledged. While in many of the great Engineering Schools of the Continentthe subject is deemed worthy of a professional chair, in England it is left to begleaned almost hap-hazard. A method more or less is thrown into a course ofteaching, according to the predilection, or dislike of the teacher for Graphic modesof procedure.

And yet the subject is valuable, not merely as a means to an end, but as a partof mental training. A mind brought up only on mathematical symbols is but halftrained: the Graphic is the complement of the Analytical process. And the powerconferred by Graphic method is to a large extent at the disposal of those who have hadbut little mathematical training. The writer once had occasion to explain a practicalapplication of the triangle of forces to a class of working men, who seemed at once tograsp and appreciate it.

The present work is an attempt to, steer a middle course between the too pro-nouncedly abstract character of many of the numerous foreign treatises, and the toonarrowly practical treatment the subject has received in England. Though con-fessedly incomplete, it will, it is hoped, prove suggestive, and may perhaps lead someof its readers to a further prosecution of a really fascinating study—one, too, in whichvery much still remains to be done.

In order to make the work self-contained, an Appendix is added, giving tables ofthe weights and strength of materials. By the help of these tables it will be foundpossible to apply the various constructions to actual practice.

The scale to which the figures are drawn is necessarily contracted, but it has beenendeavoured to make these figures clear and easy to follow.

It is perhaps necessary to apologize for the employment of a few words not yetquite naturalized in the sense here given to them. Thus “ pressure” has been adopted forcompressive stress, which has usually been termed “compression.” Using “pressure”in this sense, “ compression” is available for the alteration of length due to “ pressure.”Tension and extension are universally so used, and analogy seems to demand pressure

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