l82l.] Dr\ Rdget On Co'mpfessibUity of Water, 135 



AkTiCLfe XL 



Observations on Mr. Perkins's Account of the Compressibility of 

 Water. By P. M. Roget, MD. FRS. &c. 



(To the Editor of the Annals of Philosophy^) 



DEAR SIR, Bernard-street, ^Russel-sqiiare, Jan. 25, 182]. 



r On reading the . account which Mr. Perkins has lately given 

 •in the Philosophical Transactions,^^' of his very interesting expe- 

 riments on the compressibility of water, from which he has 

 -deduced a result differing widely from that of Mr. Canton ; and 

 being desirous of ascertaining the exact quantity by which they 

 differed, I was induced to calculate the degree of compression 

 which was produced by the piezometer in the first experiment^, 

 from the data furnished by Mr. Perkins, and was thus led to the 

 tiiscovery of a very'material error which he has committed in his 

 computation. He states the compression affected by a pressure 

 of 100 atmospheres to be " about one per cent ; " whereas the 



real amount of the compression was, in fact, only ^ , or a 



little less than one-half per cent, as may easily be verified by any 

 one who will be at the trouble of going through the calculation. 

 It is remarkable that this amended result agrees very nearly with 

 that of Canton. This will be best evinced by computing the 

 heights of the modulus of elasticity of water, in the two cases, 

 according to Dr. Young's method. As deduced from Canton's 

 experiments, the height of the modulus is 750,000 feet; f while 

 those of Mr. Perkins, when correctly computed, would show it 

 to be 743,260 feet — the difference being less than one-hundredth 

 of the whole. So near an agreement, in experiments conducted 

 by different methods, is v^ satisfactory, and bears the stronger 

 testimony in favour of the a,ccuracy of those of Mr. Perkins, in 

 as much as he was himself not aware of that agreement. It is 

 much to be wished that this gentleman, to whom science and 

 the arts are already much indebted, will persevere in the prose- 

 cution of his interesting inquiry, by the aid of the ingenious 

 apparatus he has invented, and from which the discovery of 

 many curious and important facts may be expected. 



I am, dear Sir, most truly yours, 



P. M. Roget. 



♦ For 1820, Pwrt II. p. 324. f Young's Lectures on Natural Philosaphy, i. 27 6» 



