with Fluid Object -Glasses. 283 



The attention of men of science has at last been roused to 

 this subject ; and the Royal Society of London has appointed 

 a committee for making experiments on the best method of 

 manufacturing flint-glass for achromatic telescopes. Govern- 

 ment have released the committee from the restrictions of the 

 Excise laws, and an experimental glass-house has been erected 

 for the purpose. We cannot doubt but that these experi- 

 ments will be attended with success ; but a considerable time 

 must elapse before our artists regain that advantageous posi- 

 tion which they have lost. 



Amid all these exertions to improve the achromatic tele- 

 scope, it has often struck us with surprise, that no attempt 

 has been made to introduce and to improve the achromatic 

 telescopes xoith Jluid object-glasses, invented and actually con- 

 structed by our countryman Dr Blair. The doctor himself 

 took out a patent for this valuable improvement, but practi- 

 cal difficulties were experienced in the manufacture of them 

 for sale, which prevented the patentee from ever deriving any 

 pecuniary advantage from his indefatigable and successful la- 

 bours. This, therefore, was, in a peculiar manner, a case 

 where the patronage of government was required, and where 

 it ought to have been given. From the want of such encou- 

 ragement, this invention has entirely fallen into oblivion, and 

 is now in the same state in which it was in the year 1789, when 

 it was first submitted to the public ! 



" The only philosopher, as we have elsewhere remarked, * 

 that we know of who actually looked through the telescopes of 

 Dr Blair, was Dr Robison, who always spoke of them in terms 

 of the highest praise. He informs us, indeed, that Dr Blair 

 had a telescope not exceeding Jiftcen inches in length, with a 

 compound object-glass, which equalled in all respects, if it did 

 not surpass, the best of Dollond 1 s, 4 /or£?/-too inches long. The 

 effect of this telescope, when applied to the examination of 

 double stars, was, we understand, particularly fine ; and it is 

 deeply to be regretted that Dr Blair was not encouraged, by 

 some public aid, to carry on the manufacture of such valua- 

 ble instruments. For ordinary purposes, telescopes of this 



• Edinburgh Encyclopedia, Art. Oftics, vol. xv. p. 484. 



