Some Account of the late M. Guinand, 257 



submitted to the inspection of the learned societies to which his 

 notice is addressed ; and that disk, now in the hands of the first 

 artists in London, will be the subject of one of their earliest offi- 

 cial reports*. 



Among the telescopes made by M. Guinand after his return to 

 his native country, there are several of remarkable magnitude 

 and effect; in general, the greater part appear to advantage on 

 comparison with English telescopes ; a merit which is owing in 

 an especial manner to the quality of the glass. But the most sin- 

 gular circumstance attending them is, that they have been con- 

 structed by an old man upwards of seventy, who himself manu- 



♦ Extract from the Report of the Council of the Astronomical Society of 

 London, held the 14th of February, 1824. 



" This Council have instituted some experiments on the properties of glass, 

 for the formation of the object-lenses of refracting telescopes. With this 

 view a thirty-inch telescope was constructed of some foreign glass (sent by 

 M. Guinand) for a trial of it, by Mr. Tulley. The result was satisfactory, and 

 the telescope has since been sold to one of the members. Three other pieces 

 of glass, presented to the Society by M. Guinand of Neufchatel, (one of which 

 is of a very large dimension, and promising aspect), are now undergoing trial 

 in the hands of a committee, to which the examination of their merits has 

 been referred." 



With that disk Mr. Tulley has constructed a twelve feet focal length teles- 

 cope, with which fixed stars are seen with extraordinary clearness and bril- 

 liancy. In his report to the Astronomical Society on the subject, dated Jan. 

 12, 1825, Mr. Tulley says, that owing to some peculiar circumstances he has 

 not yet quite succeeded in working the glass to his mind; and adds, "' but I 

 have no doubt I shall be able to make it into a very perfect instrument ; the 

 glass being entirely homogeneous and free from fault j the material of the 

 glass appears to me to be different from our flint-glass, as it grinds and po- 

 lishes much easier ; but whether it be harder or softer, or of a more brittle 

 nature, is of little or no importance. The ratio of the refractive and disper- 

 sive power compared with the specific gravity, seems to be lower than that of 

 the refractive and dispersive power in the British flint-glass, compared with 

 the same specific gravity. 



*• I have another piece of flint-glass 3 J inches, of (he same manufacture, 

 that seems likewise to be quite free from fault, and is as clear all over as any 

 fluid." 



It is understood that the committee will make their report upon this lena^ 

 at the next meeting of the Astronomical Society. ''* 



Vol. XIX. S 



