154 ASTRONOMY IN WANSTEAD. 



of two lenses — a form which is still in use, and known as the 

 Huygenian eyepiece. 



To erect this '■ Aerial Telescope " (as it was termed) a long pole 

 was recjuired. At the top of this a pulley was fixed, over which a 

 rope was carried ; to one end of this was attached a small travelling 

 platform, balanced on the other side by a leaden weight, the rope 

 being continued round to the lower end of ths platform. The rod 

 bearing the object glass was fitted with a "cup and ball "' joint, the 

 end of which was, when in use, inserted in a slot in the platform, 

 which was then hauled up to any height required. Then the 

 observer, holding the eyepiece by a jointed handle, pulled the long 

 connecting cord of the object glass taut, using a small winder 

 attached till the telescope was in focus, steadied his arms on a 

 wooden rest, and was then ready to make observations. 



The illustration of Huygens' Telescope here given is a reduced 

 copy of the plate in " Christiani Hugenii Zulichemii, Opera Varia 

 1728," p. 268, which is identical with the plate in his " Astroscopia 

 Compendiaria," 1684. For the loan of the book from the Library 

 of the Royal Astronomical Society, 1 am indebted to Prof. 

 Meldola, F.R.S. 



Such a telescope was a marvellous instrument indeed by com- 

 parison with those in use at that period, but being of so great a length 

 was somewhat difificult of management ; and we cannot but admire 

 the patience and skill required in its manipulation, and the dis- 

 coveries thereby accruing to the science. 



This instrument was lent for some time to Dr. Derham, at 

 Upminster, and in his preface to the ist edition of " Astro- 

 Theology," 8vo, 1715, he frecjuently makes mention of Mr. Huygens 

 glass, which he had discovered to be " an excellent glass," ^ and 

 regrets " the w'ant of a long pole to manage it." In the 3rd edition, 

 1 7 19, he also mentions the return of the Huygens' glass to the 

 Royal Society, alluding " particularly to the diligence and accuracy 

 of my very ingenious friend the Rev. Mr. Pound, into whose 

 hands the Royal Society have put their noble bequest (sic) of 

 Mr. Huygens, and who is so well accommodated for raising and 

 using that glass as to have seen (among other considerable things) 

 the five satellites of Saturn." 



Strangely enough, however, no record exists or entry of the 

 date when the Royal Society lent the telescope to Dr. Pound. 



I I'hie page 162, for his Latin inscription, with signature, scratched on tlie cihject-giass. 



