﻿Intelligence and Miscellaneous Articles, 241 



compare the general formula with observation, and which gave a sa- 

 tisfactory agreement. The value given above for - is only approxi- 

 mate. It is proved, however that the resistance of a finite cylindrical 

 conductor whose plane ends lie in two infinite insulating planes, but 

 join on to conducting masses on the further side, corresponds to a 

 length L + a of the cylinder, where 



a< 2-305 

 >fR. 



R 



10-615- 



-e" 



A 



14-771- 



-e 



4 



As a particular case, it appears that the correction to the length 

 of an organ-pipe, supposed, as in Helmholtz's paper, to be sur- 

 rounded at the mouth by a wide flange, lies between */85 K and 

 •8282 R. 



Approximate formulae are investigated for the resistance of tubes 

 which are not exact circular cylinders. It will be sufficient to par- 

 ticularize here the case of tubes of revolution. The resistance is 

 shown to lie between the two limits 

 1 Cdx 



and 



m*&) 



dXy 



where y denotes the radius of the tube at the point x. 



When there is more than one vessel in the vibrating system, 

 there are several independent periods of vibration corresponding to 

 the degrees of freedom. The theory of these vibrations is also con- 

 sidered. 



In the experimental part of the investigation the object is to de- 

 termine with sufiicient precision the pitch of the resonant note. 

 This is generally done by causing the resonator to speak. For several 

 reasons, which are detailed, I consider this course unsatisfactory, and 

 have availed myself of other indications to fix the pitch, which are 

 not, indeed, capable of so great an apparent precision, but yet are 

 more to be depended on. 



XXXII. Intelligence and Miscellaneous Articles. 



ON SOME ANALOGOUS PRINCIPLES OP PHOTOMETRY, AND THE 

 LAW OP ATTRACTION. BY W. VON BEZOLD. 



IN what follows I shall communicate a few principles of photo- 

 metry which are perfectly analogous to well-known theorems in 

 the law of attraction. The consideration of these analogies leads, on 

 the one hand, to simple solutions of many photometric problems, 

 and, on the other, to a very manifest illustration of some principles 

 of the doctrine of the potential. As the proofs for the photometric 

 principles are given in just the same manner as those for the law 

 Phil. Mag. S. 4. Vol. 41. No. 272. March 1871. R 



