OCTOBKE 19, 1900.] 



SCIENCE. 



597 



Still more nebulosity was shown by Dr. 

 Eobert's photographs,* taken with his 20- 

 inch reflector in October and December, 

 1886, when the whole western side of the 

 group was shown to be involved in a vast 

 nebula, whilst a later photograph taken 

 by MM. Henry early in 1888 showed that 

 practically the whole of the group was a 

 shoal of nebulous matter. 



In 1881 Draper and Janssen recorded the 

 oomet of that year by photography. 



Hugginsf succeeded in photographing a 

 part of the spectrum of the same object, 

 (Tebbutt's Comet, 1881, II.) on June 24th, 

 and the Fraunhofer lines were amongst 

 the photographic impressions, thus demon- 

 strating that at least a part of the contin- 

 uous spectrum is due to reflected sunlight. 

 He also secured a similar result from Comet 

 Wells. I 



I propose to consider the question of the 

 telescope on the following lines : (1) The 

 refractor and reflector from their inception 

 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 combination of the two, 

 refractor and reflector, a striking example 

 of which exists now at the Paris Exhibi- 

 tion. 



At a meeting of the British Association 

 held nearly half a century ago (1852, Bel- 

 fast) Sir David Brewster showed a plate of 

 rock crystal worked in the form of a lens 

 which had been recently found in Nineveh. 

 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 may be in- 

 ferred from the delicacy and minuteness of 

 the incised work on their seals and intagl- 



r Notices, Vol. XLVII., p. 24. 

 fProc. Boy. Soc, Vol. XXXII., No. 213. 

 tBep. Brit. Assoc, 1882, p. 442. 



ios, 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 Aris- 

 totle speaks of the tubes through which the 

 ancients observed distant objects, and com- 

 pares their eifect 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 in- 

 vented in Holland. 



The honor of being the originator has 

 been claimed for three men, each of whom 

 has had his partisans. Their names are 

 Metius, Lippershey and Janssen. 



Gralileo himself says that it was through 

 hearing that some one in France 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 dis- 

 covery, supposing such discovery to be hon- 

 estly his own, ranks as the first inventor, 

 and there is little doubt that Galileo was 

 the first to show the world how to make a 

 telescope, f His first telescope was made 

 whilst on a visit to Venice, and he there ex- 

 hibited a telescope magnifying three times; 

 this was in May, 1609. Later telescopes 

 which emanated from the hands of Galileo 

 magnified successively four, seven and 

 thirty times. This last number he never 

 exceeded. 



Greater magnifying power was not at- 

 tained until Kepler explained the theory 

 and some of the advantages of a telescope 

 made of two convex lenses in his Catoptrics 

 (1611). The first person to actually apply 

 this to the telescope was Father Scheiner, 

 who describes it in his Rosa Ursina (1630), 

 and Wm. Gascoigne was the first to appre- 

 ciate practically the chief advantages by 



*i>e Gen. Animalium, Lib. V. 

 t Newcomb's Astronomy, p. 108. 



