May 13, 1898.] 



.SCIENCE. 



653 



suggested improvements in reflecting tele- 

 scopes, and soon directed itself " to that all- 

 invincible enemy, the paucity of light in 

 powerful magnifiers. After a few moments 

 silent thought, Sir John diffidently inquired 

 whether it would not be possible to effect a 

 transfusion of artificial light through the focal 

 object of vision ! Sir David, somewhat 

 startled at the originality of the idea, 

 paused awhile, and then hesitatingly re- 

 ferred 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 refrangi- 

 bility was corrected by the second specu- 

 lum, and the angle of incidence restored 

 by the third. 'And,' continued he, 'why 

 cannot 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 antici- 

 pated the other in presenting the prompt 

 illustration that if the rays of the hydro- 

 oxygen microscope, passed through a drop 

 of water containing the larvse of a gnat 

 and other objects invisible to the naked 

 «ye, 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 distinctify (to coin a new 

 word for an extraordinary occasion) and 

 m.agnify its feeblest component members." 

 Here, indeed, was a discovery fit to 

 startle the world; and one cannot be sur- 

 prised that, after so extraordinary an ad- 

 vance, Sir John Herschel should have im- 

 mediately arranged for the construction of 

 an object-glass 24 feet in diameter. Con- 

 tributions towards this important work 

 were received from many royal personages, 

 -culminating in a gift by his Majesty the 

 King of some seventy thousand pounds. 



which was considered ample to meet all 

 expenses. Many difficulties were encoun- 

 tered 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 achromatiok discov- 

 ery of Dolland." ISTotwithstanding the 

 prodigous size of this enormous lens, which 

 weighed 14,826 pounds after being polished, 

 and whose estimated magnifying power was 

 42,000 times. Sir John was not satisfied. 

 ISTot content 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 super- 

 sede the use and infinitely transcend the 

 powers of the highest magnifiers and re- 

 flecting 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 telescope which was the first to render 

 visible the inhabitants of the Moon. It may 

 well be imagined with what breathless in- 

 terest 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 nine o'clock 

 on the night of the tenth, the Moon having 

 then advanced within four days of her mean 

 libration, that the astronomer adjusted his 

 instruments for the inspection of her eastern 

 limb. The whole immense power of his 

 telescope was applied, and to its focal image 

 about one-half of the power of his micro- 

 scope. On removing the screen of the lat- 

 ter, the field of view was covered through- 

 out its entire area with a beautiful distinct 

 and even vivid representation of basaltic 



