204 REPORT — 1855. 



for it is utterly impossible to make the notation of a machine without comprehending 

 its action in every single part. There are also many other uses, which I shall not 

 now stop to mention. The general principles of the notation are the same now as 

 in 182G ; but the practical experience of many years has, of course, suggested 

 several alterations of detail, and led to the adoption of some important principles. 



To understand the construction of a machine, we must know the size and form of 

 all its parts, — the time of action of eacli ])art, — and the action of one part on another 

 throughout the machine. The drawings give the size and form, but they give the 

 action of the parts on each other very imperfectly, and scarcely anything of the time 

 of action. The notation supplies these deficiencies, and gives at a glance the re- 

 quired information. When the drawings of a machine are made, it becomes neces- 

 sary to assign letters to the different parts. Hitherto, 1 believe, this has been left 

 much to chance; and each draughtsman has taken the letters of the alphabet, and 

 used them with little or no system. With respect to lettering, the first rules are, that 

 all framework shall be represented by tijiright letters. Moveable pieces shall be re- 

 presented by sla7iting letters. Each piece has one or more working points ; each of 

 the working points must have its own small letter, the working points of framework 

 having s7/iatl prinfed letters, and the working points of the moveable pieces having 

 small ivritten letters. 



Thus we have the machinery divided into Framing, indicated by large upright 

 letters, as A,B, C, &c. ; Moveable Pieces, indicated by large slanting letters, as A, B,C, 

 &c. ; Working points of Framing, indicated by small printed letters, as a, c, e,m,n, &c.; 

 Working points of Moveable Pieces indicated by small written letters, as a,c,e, m,7i,&c. 



In lettering drawings the axes are to be lettered first. Three alphabets may be 

 used — the Roman, Etruscan, and written, as — 



J, B, C, &c. 



A, B^ C. &c. 



These should be selected as much as possible, so that no two axes which have arms or 

 parts crossing each other should have letters of the same alphabet. Having lettered 

 the axes, all the parts on them, whether loose or absolutely fixed to them, must be 

 lettered with the same alphabet, care being taken that on each axis the parts most 

 remote from the eve shall have letters earlier in the alphabet than those parts which 

 are nearer. It is not necessary that the letters should follow each other continuously, 

 as in the alphabet ; for instance, D,L, T, may represent three wheels on the same axis : 

 D must be the most remote, L the next, and T the nearest. The rule is, that on any 

 axis, a part which is more remote from the eye than another, must invariably have a 

 letter which occurs earlier in the alphabet. By these rules very considerable in- 

 formation is conveyed by the lettering on a drawing ; but still more to distinguish 

 parts and pieces, an index on the left-hand upper corner is given to each large 

 letter; this is called the "index of identity," and all parts which are absolutely 

 fixed to each other must have the same index of identity ; no two parts which touch 

 or interfere with or cross each other, on the drawings, must have the same index of 

 identity. This may generally be done without taking higher numbers than 9. All 

 pieces which are loose round an axis must have a letter of the same character, Roman, 

 Etruscan, or writing; but a different index of identity will at once inform us that it 

 is a separate piece, and not fixed on the axis. For example, ^Z), ^L, ^T, would indi- 

 cate that the three wheels mentioned above were a\\ Ji.ved to the same axis; but 

 6Z), ^Z, 67' would at once show that D and T were fixed to the axis, and L loose upon it. 

 I shall now endeavour to explain liow the transmission of motion and action of one 

 piece on another is shown. Beginning from the source of motion, each part is 

 written down with its working points ; those of its points which are acted on are 

 placed on the left-hand side ; those points where it acts on other pieces are placed 

 on the right hand : if there are several small letters, a bracket connects them with 

 their own large letter — ru 



