PROCEEDINGS OF THE SOCIETY. 741 



It was being carefully prepared, and when complete would be a very useful 

 guide to the contents of the Library. The funds of the Society did not 

 admit of their publishing at present a catalogue, so that Mr. Eadley 

 was preparing a card catalogue arranged in a series of small boxes easy 

 of reference and easy to incorporate in their proper places the additions 

 to the Library. He was sure the Fellows of the Society would feel 

 grateful to Mr. Radley for so readily and at a considerable expenditure 

 of time undertaking this important work. 



Mr. Nelson exhibited and described an Erect-image Dissecting Micro- 

 scope by Leitz, sent by Messrs. Baker. This instrument was figured in 

 the Journal of the Society for August last,* but had not been shown at 

 any of their Meetings. The erection of the microscopic image effected 

 by means of Porro prisms, was first described by Ahrens in the Journal 

 in 1888,f and this method has since been brought into use and made 

 better known by its application to field glasses. The instrument before 

 the Meeting was valuable as a dissecting Microscope ; it was fitted with 

 hand-rests, was strongly made, and supplied with three objectives each 

 having a very long working distance. It packed up into a small box, 

 and would be found a serviceable and portable instrument. 



Mr. A. N. Disney exhibited a Diffraction plate on which the gratings 

 were ruled not in parallel lines but in concentric circles, by which the 

 diffraction bands were separated with great clearness. The rulings were 

 about 7000 to the inch. He also showed a steel brooch, the surface of 

 which had been ruled in the same way. He believed the process was 

 to be applied to the ornamentation of buttons, shirt-studs, &c, but the 

 method by which the lines were produced was at present secret. The 

 articles were of English manufacture, and had been lent to him by 

 Messrs. Townson and Mercer. 



Mr. C, F. Rousselet exhibited an Electric Lamp for use with the 

 Microscope. He said it was well known that the ordinary electric lamp 

 was quite unsuitable for microscopic work : the incandescent loop fila- 

 ment spread out in different planes and in such a way that it could not 

 be placed in the focus of a bull's-eye condenser, so that even for low 

 powers the result was unsatisfactory. As the use of the electric light 

 in private houses was becoming more general, it had always seemed to 

 him a pity that this convenient illuminaut should not be available for 

 use with the Microscope. He had, however, lately found a lamp which 

 had not the defects mentioned, and which after six months' trial he had 

 found very satisfactory for work with low and medium powers, and he 

 desired therefore to bring it to the notice of the Fellows. It was called 

 the " Focus lamp " and was manufactured by the Edison and Swan Com- 

 pany, originally, he believed, for projection work. In this lamp the 

 filament was a closely wound elongated spiral of six turns, the edge 

 view of which, when incandescent, nearly resembled the edge of the 

 flame of a half-inch paraffin lamp-wick; and by placing this edge of the 

 filament in the focus of a bull's-eye condenser, a very brilliant light was 



* Jotum. K.M.S.. 1900, p. 509. + Op. cit., 1888, p. 1020, fig. 161. 



