202 On the Fixed Lines in the Solar Spectrum. 



powers from 15 to 130 times, the object-glass of which may be 

 placed as near as may be convenient to the prism, and a 

 power of 40 or 50 times selected for the occasion ; when, how- 

 ever, the adjustment of the focal length of the telescope is 

 made to see the spectrum perfectly sharp and distinct at its 

 edges, the dark lines will be seldom seen, or, if seen at all, but 

 very faint and indistinct ; but if the drawer, or eye-piece, of 

 the telescope be pushed in about half an inch, they will then 

 be seen to perfection ; and by a nice adjustment, I have seen 

 the major part of the lines nearly as sharp and well defined as 

 the spider lines in the micrometer, employed for the measure- 

 ment of their distances from each other. 



Lambeth, 8th October, 1831. 



ON THE ACOUSTIC FIGURES OF PLATES. 

 By Professor STREHLKE. 



TN the second Number of the 8vo. vol. of Gilbert's Annalen, 

 * Professor Strehlke communicated some very interesting ex- 

 periments on this subject, which led him to conclude, 



1. That acoustic figures are composed of curves ; and 



2. That these curves do not intersect each other. 



And as Chladni had expressed some doubts on the accuracy 

 of the experiments, (chiefly on account of their having been 

 made with metallic plates,) Professor Strehlke afterwards 

 repeated them on glass plates, and convinced himself of the 

 correctness of his former experiments, and of the opinion to 

 which he was led by them. The difference between the figures 

 on metallic and on glass plates, says Professor Strehlke, when 

 speaking of his late experiments, is very trifling ; and if the ex- 

 periments are made with sufficient accuracy, the above result 

 will be equally proved by the figures on either, but the lines 

 are much more distinct on ground-glass plates, metallic plates, 

 or glass plates covered with leaf gold, than on plates of 

 polished glass ; and when he used a plate of the latter kind, 

 but covered on one side with leaf gold, the distinctness be- 



