126 THE FUNCTION OF LARGE TELESCOPES. 



at the originality of the idea, paused a while, and then hesitatingly 

 referred to the refrangibility of rays and the angle of incidence. Sir 

 John, grown more confident, adduced the example of the Newtonian 

 reflector, in which the refrangibility was corrected by the second specu- 

 lum, and the angle of incidence restored by the third. 'And,' continued 

 he, 'why can not the illuminated microscope, say the hydro-oxygen, be 

 applied to render distinct, and, if necessary, even to magnify, the focal 

 object?' Sir David sprung from his chair in an ecstacy of conviction, 

 and, leaping half-way to the ceiling, exclaimed, 'Thou art the man!' 

 Each philosopher anticipated the other in presenting the prompt illus- 

 tration that if the rays of the hydro-oxygen microscope, passed through 

 a drop of water containing the larv?e of a gnat and other objects invis- 

 ible to the naked eye, rendered them not only keenly distinct, but 

 firmly magnified to dimensions of many feet, so could the same artificial 

 light, passed through the faintest focal object of a telescope, both dis- 

 tinctify (to coin a new word for an extraordinary occasion) and magnify 

 its feeblest component members." 



Here, indeed, was a discovery fit to startle the world; and one can 

 not be surprised that, after so extraordinary an advance, Sir John 

 Herschel should have immediately arranged for the construction of an 

 object glass 24 feet in diameter. Contributions toward this important 

 work were received from many royal personages, culminating in a gift 

 by His Majesty the King of some £70,000, which was considered ample 

 to meet all expenses. Many difficulties were encountered in casting 

 the great object glass, which was composed of " an amalgamation of 

 two parts of the best crown with one of flint glass, the use of which in 

 separate lenses constituted the great achromatick discovery of Dollond." 

 Notwithstanding the prodigious size of this enormous lens, which 

 weighed 14,82G pounds after being polished, and whose estimated mag- 

 nifying power was 42,000 times, Sir John was not satisfied. Not con- 

 tent with the mere illuminating power of the hydro-oxygen microscope, 

 "he calculated largely upon the almost illimitable applicability of this 

 instrument as a second magnifier which would supersede the use and 

 infinitely transcend the powers of the highest magnifiers and reflecting 

 telescopes." Indeed, so certain was he of the successful application of 

 this idea that he counted upon "his ultimate ability to study even the 

 entomology of the moon in case she contained insects upon her surface." 



It would be interesting, if time permitted, to consider with our 

 inspired author the various further details in the construction of a tele- 

 scope which was the first to render visible the inhabitants of the moon. 

 It may well be imagined with what breathless interest the report of Sir 

 John's extraordinary discoveries, which constitutes the body of our 

 pamphlet, was received by a willing public. "It was about half-past 9 

 o'clock on the night of the 10th, the moon having then advanced within 

 four days of her mean libration, that the astronomer adjusted his instru- 

 ments for the inspection of her eastern limb. The whole immense power 



