Dimensional Properties of Matter in the Gaseous State. 103 



themselves. Thus, after the first particle appears, it must 

 remain at its brightest incandescence until all the material of 

 which it is composed is precipitated. From this we see that 

 such a horizontal current must increase gradually in brilliancy 

 to its maximum, and then suddenly diminish — an exact 

 accordance with the facts as observed, 



Jolms Hopkins University, 

 Baltimore, Sept. 1880. 



XIV. On Professor Osborne Reynolds's Paper " On certain 

 Dimensional Properties of Matter in the Gaseous State.'''' 

 By George Feancis Fitzgerald, M.A., F.T.C.D* 



THE Royal Society has published in its Philosophical 

 Transactions, 1879, part ii., a valuable and interesting 

 paper by Prof. Osborne Reynolds, " On certain Dimensional 

 Properties of Matter in the Gaseous State." In it he first 

 calls attention to the phenomenon of " Thermal Transpiration," 

 and professes to give not only explanations of this and allied 

 phenomena, but also the means of calculating their amounts. 

 The late Prof. J. Clerk Maxwell expressed his obligation to 

 Prof. Reynolds for having directed his attention to this phe- 

 nomenon, and to the necessity of investigating the conditions 

 at the surface of separation of a solid and a gas. At the same 

 time he expresses himself dissatisfied with Prof. Reynolds's 

 investigation, although he does not point out what parts he 

 considers faulty. As Prof. Reynolds's paper is very elaborate, 

 and necessarily somewhat difficult, not only from the nature 

 of the subject, but also, in parts, owing to the inelegant 

 method that Prof. Reynolds has pursued, it may be of in- 

 terest to the readers of the Philosophical Magazine to have 

 some objections to his investigation pointed out, in order that 

 Prof. Reynolds may have an opportunity of refuting them, 

 and also in order that the doubts that Maxwell has raised as 

 to the real value of the investigation may be shown either not 

 to apply, or at least not to affect the essence of the results. 



In the first place I must express my entire admiration for 

 the first part of the paper, dealing with experiments. These 

 were conducted both carefully and scientifically. They are 

 not of that haphazard character so much in vogue with un- 

 scientific experimenters. Each is framed for the purpose of 

 illustrating, verifying, or investigating some definite theory. 

 Maxwell's objections, then, can only have referred to Part II. 

 (Theoretical), beginning at § 53. Against this paragraph I 

 desire to enter a protest, because it seems to assert that some 

 other theories of the action of the radiometer widely different 

 Communicated by the Author. 



