London Electrical Society. 245 



Society upon its performance. Mr. King now states that the result 

 of numerous observations on a variety of objects leads him to con- 

 sider this glass as one of much excellence, though not faultless. 

 There is scarcely any spherical aberration, and the light is very 

 white and free from colour ; but when the central portion is co- 

 vered up, there is a good deal of irradiation, indicating a want of 

 homogeneity near the edge of the lens, where the glass is very thick. 

 For many objects, however, especially very faint nebulae, the whole 

 aperture may be used with great advantage ; but for most purposes 

 a contraction to six inches, or a little less, causes it to perform 

 much better, and enables it to carry high powers with much distinct- 

 ness. The powers tried with it vary from 40 to 700, and no doubt 

 it would satisfactorily bear a considerable increase in this respect. 

 It is not saying much of such an object-glass, that the small stars 

 accompanying Polaris, a Lyra;, and Rigel, are readily seen ; but it 

 shows also with the greatest distinctness and completely separates 

 the close stars of £ Cancri, i and £ Bobtis, £ Ursa, &c, and also 

 8 Cygni, which affords one of the best tests of distinctness and per- 

 fection in a telescope. As a planetary glass, Mr. King remarks that 

 he cannot speak of it so decidedly, not having had a fair opportunity 

 of trying it. Jupiter and Saturn have both for a long time been at 

 very low altitudes, and, with respect to his observatory, the entire 

 range of each is through the smoke of London. But with the moon 

 it performs magnificently, penetrating, as it would seem, into her 

 very structure, when high magnifying powers are used. Upon the 

 whole, he is of opinion that this object-glass will bear compari- 

 son with most others of the same size worked from the foreign 

 material. 



The object-glass is fitted into a brass cell, admitting of accurate 

 adjustment by means of three screws with rods reaching to the eye 

 end. The telescope, twelve feet in length, is mounted upon the 

 rotative roof of a small observatory, in a manner which combines 

 great ease in observing with freedom and steadiness of motion. 



LONDON ELECTRICAL SOCIETY. 



July 20, 1841. — The communications before the Society were, — 

 1st, " On the Perforation of Non-conducting Substances by the 

 Mechanical Action of the Electric Fluid." By Mr. Crosse. 



Two wires were laid end to end and tied firmly on a piece of 

 window glass, and a quick succession of sparks was passed be- 

 tween them by connexion with the respective conductors of a power- 

 ful machine ; the result was a perforation. The same was varied 

 in several ways ; and was afterwards successfully tried with a cry- 

 stal of quartz. The author concludes that even diamonds may be 

 thus drilled. 



2nd. " The Effects of Vegetable Points on Free Electricity." By 

 Mr. Pine. 



