152 Intelligence and Miscellaneous Articles. 



means of a solar microscope, an image o£ the shadow of the plati- 

 num plate was thrown upon a screen. The bounding line of the 

 shadow, as nearly as possible straight, was condensed by a cylin- 

 drical lens. In the place of the screen a glass plate, prepared with 

 Vogel's emulsion, was now moved rapidly across by a strong 

 spring, so that the direction of its motion was perpendicular 

 to the line of light produced by the cylindrical lens, while the 

 mouthpiece was spoken into. Side light being duly kept off, a 

 bounding line between light and shadow was then obtained on the 

 prepared plate, forming a curve corresponding to the sonorous 

 vibrations. To the vowels pretty simple curves correspond, often 

 approximately curves of sines, often interference-curves of two or 

 three curves of sines. With the vowel a a period contains the 

 greatest, with the vowel u the least number of indentations. To 

 the consonants I, m, n, r, and also especially p and k, uncommonly 

 multifarious curves correspond, having a resemblance to those found 

 by Konig for r by means of his tone-flame, but showing in addition 

 much finer details. 



The author intends to repeat the experiments by photography 

 upon rotating disks in order to be able to take up a greater number 

 of successive vibrations.—- -Kaiserl. Akacl. cler Wissensch. in Wien, 

 maih.-naturw. Classe, Nov. 30, 1882. 



ON CENTRAL FORCES AND THE CONSERVATION OF ENERGY. 

 To the Editors of the Philosophical Magazine and Journal. 



GrENTLEMEN, 



Permit me to point out an error in Mr. Browne's paper with 

 the above title in the January number of the Philosophical Maga- 

 zine. On page 37 he says, " Then it is easy to show that F must 

 not vary with 0. For if it does, let us suppose that when B has 

 come to rest, and before it is allowed to return, it is made to rotate 

 about A through an angle dd, and again brought to rest. Then 

 the circumstances of A and B are unchanged." This last state- 

 ment is only true if F, the component of the force in the direction 

 AB, constitutes the whole force ; for otherwise work will be done 

 during the rotation, and therefore the potential energy of the 

 system will be changed. Thus Mr. Browne's conclusion that " the 

 force with which A acts upon B always tends towards A," is tacitly 

 assumed in the proof. It therefore appears to me that the only 

 conclusion which Mr. Browne is entitled to draw is that if the 

 force with which A acts upon B always tends towards A, then its 

 magnitude must be a function of the distance only. 



I have the honour to remain, Grentlemen, 

 Tour obedient servant, 



Gr. W. VON TUNZELMANN, 



H.M S. i Britannia? Dartmouth. 



