16'8 - OBSERVATIONS ON NEBULA 



tioned, which passed down to a windlass at the base, while a slow motion was 

 gained by an apparatus very similar to that described and figured in Pearson's 

 Astronomy as attached to Ramage's telescope — a combination of ropes within 

 the immediate command of the observer. In azimuth the whole frame could 

 be wheeled about by a single person, and a slower motion was obtained by 

 simply swinging the telescope by the hand, which could be done by the ob- 

 server, in following a star, with perfect steadiness. At very high altitudes, the 

 system of ropes was not available ; but the weight of the upper end of the tele- 

 scope was then so little that the observer could grasp the tube in his arms, 

 steadying them by contact with the converging beams, and carry on his work 

 nearly as well as before. This method of directing a large telescope is much 

 ruder in description than in practice. 



A light frame-work of steps, detached from the main frame, served to sup- 

 port the observer in his elevated situation. Against this the tube of the tele- 

 scope could be steadied at any moderate elevation, by means of a simple con- 

 trivance ; this, however, was never necessary unless in high winds. The tube 

 was, at first, of wood, but was afterwards replaced by sheet iron, on account of 

 its superior lightness and portability; it was painted outside and inside, and 

 protected, during bad weather, by oil-cloth, the speculum at such times being 

 taken out. 



5. It was our intention, at first, to have availed ourselves of the power and 

 light of this instrument in a meridional review of a portion of the double stars 

 of the younger Herschel's catalogue. But a short experience convinced us 

 that its large surface was much better adapted to observations on the fainter 

 nebulae than its power of separation to the examination of close double stars. 

 And an imperfection in the casting,* which, in spite of the most patient endea- 

 vours in renewed and frequent polishing, seemed to vitiate a portion of the 



* It is exceedingly difficult to obtain a good casting of so large a speculum. The metal, in 

 itself, is of a composition that presents obstacles of no ordinary difEculty, while, from the compa- 

 rative ignorance and unskilfulness of many of our workmen in this department, those facilities are 

 not afforded for overcoming these obstacles which scientific interest in Great Britain and the older 

 countries of Europe has conferred. For a telescope considerably less in size I have had more than 

 fifty specula cast before I could obtain one free from imperfections, and susceptible of a very ex- 

 cellent figure. In the present case, the general figure of the speculum, except in the neighbour- 

 hood of the flaw I have spoken of, seemed to be excellent. 



