July 13, 1876] 



NATURE 



233 



THE KINEMATICS OF MACHINERY' 



II. 



A FTER the discussion of lower pairs of elements, 

 -^ *- higher pairs are considered, such, for instance, as 

 that of the duangle and triangle, the motions of which 

 with respect to each other are thoroughly described. 

 One of the most useful sections of the book, and which 

 we strongly recommend to the attention of engineers and 

 machinists, is that on the General Determination of Pro- 

 files of Elements for a given Motion (p. 146). To the 

 practical mechanic who has read the discussion ou the 

 different pairs of elements, it must appear that there are 

 some motions taking place in machines in the required 

 manner that are not constrained completely by the resist- 

 ance of the parts of the machine, such, for example, as 

 the motion of the bed-plate of a planing machine in the 

 V guides, and it is obvious that this motion would not be 

 constrained to take place in the required manner if the 

 machine were turned upside down. The constraint only 

 in certain positions of the pair of elements is called force 

 chsuft', and the pair is called an incomplete pair of 

 elements, the determination of the motion in the required 



Fig. 5. 



manner being effected only with the assistance of the 

 weight of one element, which must be greater than any 

 disturbing force tending to cause motion in the direction 

 opposite to that in which its weight acts. As examples 

 of force-closed pairs are mentioned the plummer block of 

 a water-wheel, which, owing to the weight of the wheel, 

 constrains the motion without the complete closure of the 

 pair by the addition of the cap, also railway wheels with 

 the metals on which they roll. 



We pass now to the History of Machine Development. 

 " At the commencement of a study of machine develop- 

 ment it is first of all necessary to know distinctly what it 

 is that makes a machine complete or incomplete. It is 

 only possible to judge of the completeness of a machine 

 from the excellence of the work produced by it, if we 

 are able to estimate separately what part of the result 



' "The Kinematics of Machinery : Outlines of a Theory of Machines." 

 By K. Reuleaux, Director of and Professor in the Kiiniglichen Gewerbe- 

 Akademie in Berlin, Member of the Konigl. technischen Deputation fiir 

 Gewerbe. Translated and edited by Alex. B. W. Kennedy,^ C.E., Professor 

 of Civil and Mechanical Engineering in University College, London. 

 (London : Macmillan and Co., 1876.) Continued from p. 214. 



is due to the skill of the workman. Certain Indian 

 fabrics, for instance, are of extraordinary excellence and 

 delicacy, although they have been made in most defective 

 looms ; throughout the whole manufacture of these it is 

 the weaver's dexterity that plays the most important part. 

 In no machines can we absolutely do away with human 

 action, if it be for no further purpose than to start 

 and stop the process. It appears, therefore, that the 

 most complete machine is the one fulfiUing best its own 

 work, and having for this share the greatest proportion 

 of the whole task." The great use of tracing the history 

 of the development of machines is, that the more clear 

 the path along which real advance has come to pass can 

 be laid down, the more clearly we are enabled to see the 

 direction that must be taken by succeeding advances. 

 Piobably the earliest machine known is the fire-drill, used 

 in very early days of the development of the human race 

 for producing fire by its rapid rotation between the hands, 

 being at the same time held in firm contact with another 

 flat piece of wood. The improvements on this appear to 

 have been pointing the fire-drill at the other end, en- 

 abling the vertical pressure to be supplied by an assistant 

 by means of a flat piece pressed on the top of the drill, 



and communicating the rotation to the drill by means oi 

 a cord wrapped once or twice round it. The applications 

 of this tool seem to have been numerous, as with it hard 

 woods, bone, horn, and even hard stones, appear to have 

 been drilled, no doubt with the assistance of a supply of 

 sand and water. From the fire-drill, probably after a 

 very long interval, sprang the potter's wheel, and the 

 earliest forms of turning-lathe turned in a similar manner ; 

 the principle is preserved to the present day in the bow- 

 drill used for light metal-work. The origin of the screw 

 and nut is lost in obscurity, but this pair of elements 

 was certainly known to the Greeks and Romans ; Prof. 

 Reuleaux's suggestion of its origin, tracing it to the fire- 

 drill, is very ingenious, even if it is not the right one ; that 

 with long-continued use of the drill, the' cord may have 

 worn spiral groves on the spindle, forming a screw-thread 

 while the cord itself formed the nut. " The forms of the 

 word screw in the Germanic languages greatly strengthen 

 my suggestion. We cannot take into account the fact 

 that in English and the Romance languages the charac- 

 teristic portion of the screw is called ' thread' {flo, filet), 



