404 REPORT— 1892. 



with continuity, and they lend themselves better than any other form to 

 the juncture between any curve whatever. 



2. A portion of a curve being given, one can find rapidly the centre 

 of curvature without using the compass. 



3. The development of a given curve can be rapidly constructed 

 without using a compass or rule. 



4. Calculations can be readily performed with it. 



A very interesting class of modern instruments, called ' integraphs,' 

 has been invented by Mr. Abdank Abakanowicz and Mr. Vernon Boys. 

 These instruments di'aw what is known as the ' integral curve ' when a 

 pointer is passed round the periphery of a figure whose area is required.' 



3. Self-recording Instruments. 



There is no class of instruments which have increased to such a great 

 extent as those which record their own results in the form of a curve or 

 mark of some kind. An instrument of this kind may be used for an 

 almost countless variety of purposes, but many of them have certain 

 features in common, or difier in certain important particulars, which 

 enables the subject to be considered under a comparatively limited number 

 of heads. 



1. All instruments have some kind of markinsr arranjrement, and 

 some kind of prepared surface on which the record is made. 



2. Almost all instruments of this kind have some contrivance for 

 giving motion to the surface upon which the record is obtained, and this 

 motion corresponds to the change in one of the two variable quantities 

 which are to be recorded. 



3. The marking arrangement, which makes the record, is actuated by 

 means of some mechanical contrivance so as to correspond in position to 

 the magnitude to the other variable quantity. 



These facts supply the headings under which the subject may be 

 studied. 



1. The arrangement for marking may consist of — 



a. Pricker, which makes a puncture or mark of some kind at 



certain intervals. 

 h. Pencil drawing upon ordinary paper. 



c. Metallic pencil drawing upon prepared paper. 



d. Twisted spiral of one convolution marking the surface in con- 



tact with it. 



e. A style scraping a surface of smoked paper or glass, or some other 



prepared surface. 

 /. Pens writing a record with some kind of ink. 

 J/. Siphon-recorder of Sir William Thomson. 

 h. A spot of light reflected from a mirror acting upon a chemically 



prepared surface. 



Of course, nothing but practical results can decide which is the most 

 suitable of all these for any particular purpose, and, from inquiries which 

 the writer has made, it appears that a great difference of opinion exists 

 on the subject. 



' Les Intcgrajyhes, by Mr. Abdank Abakanowicz. Gauthier-Villars, Paris, 1886. 

 ' Integrators,' by C. Vernon Boys, Phil. Mag., 1882. 



