TRANSACTIONS OF THE SKCTIONS. 205 



' The pieces being arranged, arrow-headed lines join each acting or driving point 

 of one piece with the point of another piece, which it drives or acts on. When a 

 machine is complicated, it is usually necessary to make two or three editions before 

 all the parts can be arranged with simplicity ; but, when done, the Trains, as they 

 are called, indicate with the utmost precision the transmission of force or motion 

 through the whole machine, from the first motive power to the final result. It is, 

 however, one of the principles of the notation to give at one view tlie greatest possible 

 amount of information, provided that no confusion is made ; it has been found that, 

 without in any way interfering with the simplicity of the Trains, a variety of infor- 

 mation on other points may be conveyed. For instance, whilst looking at tlie Trains, 

 it is often convenient or necessary to know something of the direction of motion of 

 the piece under consideration, and, by the use of a few signs placed under the large 

 letters, we can convey nearly all that is wanted in this respect. Again, though the 

 drawings of a machine are specially intended to give the size and shape of each piece, 

 yet by the use of some signs of form which are placed above the letters, the form of 

 each piece may be indicated. It is found that these signs do not confuse the Ti-ains ; 

 but, on the contrary, extend their use, by making the information they convey more 

 condensed, and more easily accessible. 



I now pass on to the Cycles, as they are termed, or to that part of the notation which 

 relates to the time of action of the different parts of a machine. The cycles give 

 the action of every part during the performance of one complete operation of the 

 machine, whatever that may be. Each piece has a column of its own, and the points 

 by which it is acted on are placed on its left hand, and the points by whicli it acts 

 on other parts are placed on its right ; and each working point also has its own 

 column. The whole length of the column indicates the time occupied in performing 

 one operation, and we divide that time into divisions most suited to the particular 

 machine. During each division of time that a piece is in motion, an arrow up or down 

 its column indicates the fact; and during the time of action of each working point, 

 an arrow in its own column shows the duration of its action. The times thus shown 

 are, of course, only relative, and not absolute time ; but it would be easy to show both, 

 by making the divisions of the columns correspond with the number of seconds or 

 minutes during which the machine performs one operation. The arrows which point 

 upwards indicate circular motion in the direction, screw in, and the arrows which 

 point downwards, screw out; where the motion is linear, the downward arrow indi- 

 cates motion from right to left. 



Mr. Babbage then illustrated this system of notation by directing attention 



to the notation of the Difference Engine of Messrs. Schelitz. This machine contains 



several hundred different pieces, yet the trains showed at one view how each piece 



•was acted on, and how it acted on other pieces ; the Cycles gave with equal clearness 



Ithe time of action of each piece. In fact, the two pieces of paper before the Section 



jgave a complete description of the machine, and, with the drawings, rendered further 



explanation unnecessary. 



On an Instrument for Sounding. By Robert Barklay. 

 The principle is based upon the compressibility and elasticity of vulcanized india- 

 rubber discs subjected to the pressure of the fluid on all their sides, the reduction of 

 ^ their bulk laterally by the pressure being indicated upon a scale, while their tempera- 

 ture may be kept equable by the instrument being submerged for a time. 



On Continuous Work in Dockyards, By Lady Bentham. 



On the Mechanical Principles of Ancient Tracery. 

 By Robert W. Billings. 



On the Importance of Periodical Engineering Surveys of Tidal Harbours, 

 illustrated by a comparison of the Surveys of the River Mersey, by the late 

 Francis Giles, C.E., and by the Marine Surveyor of tlie Port of Liverpool. 

 By Joseph Boult, Liverpool. 



