90 Mr. Galloway's Remarks on Fernel's Measure of a Degree. 



The investigation I have now gone through opens a very 

 extensive field of inquiry, which I hope to be able to prosecute 

 at some future opportunity. In the mean time I consider 

 myself entitled to say, that the solution I have given of the pro- 

 blem of the resistance of the air to an oscillating sphere iscoi*- 

 rect, since it takes account of the condition expressed by 

 equation (4.); and that Poisson's is at fault by neglecting this 

 condition, and consequently depending on an equation of in- 

 sufficient generality. It would not be difficult to show that 

 the equation in ^ which Poisson makes use of, applies only 

 to instances in which a surface of displacement coincides with 

 a surface of equal pressure, which is by no means the case in 

 every instance of fluid motion. 

 Cambridge Observatory, Dec. 17, 1841. 



XVI. Remarks on Fernel's Measure of a Degree. 

 By Thomas Galloway, A.M., F.R.S. 



To the Editors of the Philosophical Magazine. 



Gentlemen, 

 BEG to offer a few remarks on Fernel's measure of the 

 terrestrial degree, partly in reply to Professor De Mor- 

 gan's letter which appeared in the Number of your valuable 

 Magazine for December last, and partly for the purpose of 

 pointing out some mistakes into which Lalande has fallen in 

 treating of the same subject. 



The most important point in Mr. De Morgan's letter is that 

 which concerns Montucla and Delambre. Montucla reports 

 the result of Fernel's measure of the degree to be 56,746 French 

 toises ; Delambre makes it 57,070 toises ; and Mr. De Morgan 

 says, that " in looking over the work of Fernel he was sur- 

 prised to see that he himself states a very different result," 

 namely, 68 Italian miles and 96 paces ; and calls the atten- 

 tion of mathematicians to the circumstance as showing how 

 the history of science is sometimes written. Coming from so 

 hi'^h an authority, an implied charge of inaccuracy against two 

 authors whose works are in the hands of every student, and 

 whose statements are so generally trustworthy, demands some 

 investigation. 



Mr. De Morgan has cited from the Cosmotheoria three dif- 

 ferent passages in which the result is expressed in Italian miles, 

 but there is still another passage in the same work (forming, 

 indeed, part of the same sentence from which the third cita- 

 tion is made), in which the result is otherwise expressed, and 

 accompanied with details which appear to me to be equally 



I 



