204 Prof. A. W. Elicker on the Density and 



Fitzgerald mentioned that in his lectures he had spoken of 

 matter as possibly travelling through space in the same way 

 that a drop of water travels through a block of ice. The idea 

 involved is the same as that which forms the basis of the fore- 

 going pages. I have availed myself of Professor Fitzgerald's 

 criticism to amend some remarks contained in the earlier part 

 of the paper, and there is just one thing more which I should 

 like to add. Every opinion expressed in the paper is not to 

 be taken as an essential part of the theory, and, indeed, the 

 most I can hope from an investigation so obviously incomplete 

 is that it may prove suggestive to those who are working 

 at the subject. 



XIX. On the Density and Composition of Dilute Sulphuric 

 Acid.— No. II. By A. W. Ruckeb, M.A., F.R.S.* 



IN a paper on the " Densities of Sulphuric-Acid Solutions/' 

 which appeared in the January number of this Magazine, 

 Mr. Pickering has replied to my criticism of one of his curves, 

 which was published in September (Phil Mag. Sept. 1891, 

 p. 304). I propose as briefly as possible to indicate the 

 points in which he traverses my arguments, and the reasons 

 why I do not think that his conclusions are justified. 



(1) Mr. Pickering objects that my equation is " of a com- 

 plex and highly artificial form." The question as to what is 

 a " complex " expression may be more or less a matter of 

 opinion. I can only say that I think Mr. Pickering will 

 find that my equation lends itself to numerical computation 

 much more easily than 



y = a + bx + ex 2 + dx d + ex 4 +fx 5 -f gx G , 



which he seems to consider comparatively simple. 



He is also probably aware that eveiy time he applies his 

 bent ruler to the paper, he is employing a curve of which the 

 equation involves elliptic integrals and is far more complex 

 than that to which he objects. 



Of course he might reply that the short portions of the 

 elastic curve which he uses might be expressed with sufficient 

 accuracy by simpler approximate formulae. If this argument 

 were valid, I might point out that he could get still simpler 

 results and reduce all his curves to straight lines if he carried 

 the process of subdivision further. It is in general the case 

 that an equation which represents a long range of experi- 

 ments will be more complex than one which applies to a 

 few only. This affords no argument against its use as an 



* Communicated by the Author. 



