342 Mr. C. V. Boys on an Integrating-Macliine. 



I think that now Mr. Fitzgerald will reconsider his protest 

 against § 53 ; for while maintaining, on the one hand, a theory 

 fundamentally different from that in my paper, he can hardly 

 maintain, on the other, that there are no such theories, and 

 that they have not found supporters. But, in truth, the 

 remark in art. 53 was not applied to the theory which Mr. 

 Fitzgerald seems to he supporting ; and as I am sure that he 

 is not prepared to maintain that the phenomena of the radio- 

 meter take place in an absolute vacuum, or are due to the 

 same cause as gravitation, I am sure that he will not wish to 

 stand sponsor to all the thoories set forth since 1874. 



In conclusion, I would say one word in acknowledgment of 

 those remarks in Mr. Fitzgerald's paper that were the reverse 

 of critical, and to confess that it is a matter of no small satis- 

 faction to have found a reader of Mr. Fitzgerald's knowledge 

 and acumen. 



Owens College, 



March 24, 1881. 



XLYII. An Integrating-Macliine. 



By C. V. Boys, Assoc. Royal School of Mines.* 



[Plate VIII.] 



ALL the integrating-machines hitherto made of which I 

 can find any record may be classed under two heads : — 

 one, of which Amsler's beautiful instrument is the sole repre- 

 sentative, depending on the revolution of a disk which partly 

 rolls and partly slides on the paper ; the other, comprising 

 all the remaining machines, depending on the varying dia- 

 meters of the parts of a rolling system. As this subject has 

 been treated so recently by Mr. Merrifield in his " Report on 

 the Present State of Knowledge of the Application of Qua- 

 dratures and Interpolation to Actual Data," read at the meet- 

 ing of the British Association at Swansea, 1880, in which he 

 briefly describes previous machines and refers to the papers 

 in which a full description may be found, I do not think it 

 advisable to say more concerning them, except that none of 

 them do their work by the method of the mathematician, but 

 in their own way. The machine, however, which I have the 

 honour of bringing before the notice of the Physical Society 

 is an exact mechanical translation of the mathematical method 

 of integrating y dx, and thus forms a third type of instrument. 

 The mathematical rule may be described in words as fol- 

 lows : — Required the area between a curve, the axis of x, and 

 two ordinates. It is necessary to draw a new curve such that 



* Communicated by the Physical Society, having been read at the 

 Meeting on February 26. 



