666 REPORT— 1900, 



In 1881 Draper and Janssen recorded the comet of tbat 3'ear by pbotogTaphy. 



Hu"'^ins * succeeded iu photographiiif^ a part of tlie spectrum of the same 

 object, (Tebbutt's Comet 1881 ,11.) ou June 24, and the Fraunbofer lines were amoni^st 

 the photographic impressions, thus demonstrating tbat at least a part of the 

 continuous spectrum is due to reflected sunlight. lie also secured a similar 

 result from Comet Wells.- 



I propose to consider the question of the telescope on the following lines : 

 (1) The refractor and reflector from their ince]>tion to their present state. (2) The 

 various modifications and improvements that have been made in mounting these 

 instruments, and (3) the instrument that has been lately introduced by a com- 

 bination of the two, refractor and reflector, a striking example of which exists now 

 at the Paris Exhibition. 



At a meeting of the British Association held nearly half a century ago (1852) 

 (Belfast) Sir David Brewster showed a plate of rock crystal worked in the form 

 of a lens whicli had been recently found in Isineveh. Sir David Brewster asserted 

 that this lens had been destined for optical purposes, and that it never was a dress 

 ornament. 



That the ancients were acquainted with the powers of a magnifying lens 

 maybe inferrerl from the delicacy and minuteness of the incised work on their 

 seals and intaglios, which could only have been done by an eye aided by a lens of 

 some sort. 



There is,' however, no direct evidence that the ancients were really acquainted 

 with the refracting telescope, though Aristotle speaks of the tubes through which 

 the ancients observed distant objects, and compares their efl'ect to that of a well 

 from the bottom of which the stars may be seen in daylight.^ As an historical fact 

 without any equivocations, however, there is no serious doubt that the telescope 

 was invented in Holland. 



The honour of being the originator has been claimed for three men, each of 

 whom has had his partisans. Their names are Metius, Lippershey, and Janssen. 



Galileo himself says that it was through hearing that some one in Fr.mce or 

 Holland had made an'instrument which magnified distant objects that he was led 

 to inquire how such a result could be obtained. 



The first publisher of a result or discovery, supposing such discovery to be 

 honestly bis own, ranks as the first inventor, and there is little doubt that Galileo 

 was the first to show the world how to make a tele.scope.'* His fir.st telescope was 

 made whilst on a visit to Venice, and he there exhibited a telescope viafpufi/ing 

 three times: this was in May ] GOO. Later telescopes which emanated from the 

 hands of Galileo magnified successively four, seven, and thirty times. This latter 

 number he never exceeded. 



Greater magnifying power was not attained until Kepler explained the theory 

 and some of the advantages of a telescope made of two convex lenses in his 

 Catoptrics {IQW). The first person to actually apply this to the telescope was 

 Father Scheiner, who describes it in his Bosa Ursina (1630), and^Vm. Gascoigne 

 was the first to appreciate practically the chief advantages by his invciition of the 

 micrometer and application of telescopic sights to in>trumeiits of precision. 



It was, however, not until about the middle of the seventeenth .entury that 

 Kepler's telescope came to be neaily universal, and tlien chiefly because its field 

 of view exceeded that of the Galilean. 



The first powerful telescopes were made by Iluyghens, and with one of these 

 Le discovered Titan (Saturn's brightest satellite) :" his telescopes magnified from 

 fortv-eight to ninety-two times, were about 2^ inches aperture, with focal lengths 

 ranging from 12 to 23 feet. By tlie aid of these he gave the first explanation of 

 Saturn's ring, which be published in 1659. 



Huyghens also states that be made object-glasses of 170 feet and 210 feet focal 

 length ; also one 300 feet long, but which magnified only 000 times ; he ako 

 presented one of 123 feet to the Royal Society of London. 



> Proc. Roy. Soc, vol. xxxii. No. 213. = Bep. Brit. Assoc, 1882, p. 442. 



^ Pfl Gen. Animalium, lib. v, •* Newcomb's A.itnmomy, p. 108. 



