348 Dr. C. R. A. Wright on the Determination of 



point distant from e e by an amount equal to <j>x yfrx ; if, then, 

 the front wheel of the cart is kept at right angles to a line 

 joining this point of intersection with a point on ee distant 

 from the upper axis of x by an amount equal to k or 1, then 



the cart will draw the line y—\ <j>x yfrx dx. The same prin- 



Jo 

 ciple might be applied to integrate the product of more than 

 two functions. 



As in the case of simple functions, so with squares, cubes, 

 and products, the reciprocal could be integrated by twisting 

 the plane of the front wheel of the cart through a right angle. 



Also the integral of 2£l comc i ^ f ounc i ^ making the lower 



curve y=yfrx, the upper curve y = <j>x, and by keeping the rod 

 which passes through the upper tracing-point parallel instead 

 of at right angles to A B. 



The axis of x is drawn by using a little J square of such a 

 length that its end is the same distance from the edge of the 

 board as the fixed centre B ; then a pencil held at the end 

 while the square is moved across the board will at once give 

 the axis of x. 



I do not consider the modifications of the machine to be 

 of much importance ; but the simple machine as described 

 in the first part of this paper, is, I think, interesting as being 

 the only one that really illustrates the mathematical formula for 

 the integration of y dx. 



My thanks are due to Mr. Hilger, of Tottenham Court 

 Road, for the great care and skill which he has bestowed upon 

 the construction of the instrument. Certain modifications of 

 detail, however, have been introduced which make it more 

 easy of manipulation without sacrifice of simplicity. 



Physical Laboratory, 

 South Kensington. 



XLYIII. On the Determination of Chemical Affinity in terms of 

 Electromotive Force. — Part IV. By C. R. Alder Wright, 

 D.Sc. (Lond.), Lecturer on Chemistry and Physics in St. 

 Mary's Hospital Medical School. 



[Concluded from p. 283.] 

 Effect of Variation of the Material of the Electrode. 

 90. TT is well known, from the experiments of previous ob- 

 J- servers, that the nature of the surface of the electrode 

 considerably affects the value of the counter E.M.F. set up, 

 and that in particular platinizing a platinum electrode largely 

 decreases the counter E.M.F. set up by a given current. 



