1867.] Rev, Di\B.ohmson on the Melbourme Telescope. 159 



It deserves, moreover, to be mentioned that a compound isomeric with 

 methyhc aldehyde, the dioxymethjlene (C^H^OJ of M. Boutlerow, is 

 known ah'eady ; also that a sulphur-compound of the formula 



CH,S 



has been obtained by M. Aime Girard, who observed that bisulphide of 

 carbon is reduced by the action of nascent hydrogen with disengagement 

 of sulphuretted hydrogen. 



In the course of next winter I propose to perform some further experi- 

 ments on the product of the slow combustion of methylic alcohol for the 

 purpose, if possible, of isolating methylic aldehyde in a state of purity, and 

 of thus completing this inquiry. 



VII. On the New Reflecting Telescope to be used at Melbourne, 

 Australia.''^ In a Letter to the President. By the Kev. Dr. 

 Robinson, F.R.S. Received October 15, 1867. 



Observatory, Armagh, October 14, 1867. 

 My dear Feiend, — As you express a wish to know my recent impres- 

 sions respecting the great telescope, I can say that they are very satisfac- 

 tory. When I saw it six weeks ago the first of the two great specula was 

 just polished ; and though the essential parts of the equatoreal were in 

 position, and one could estimate the facility with which it could be managed, 

 the optical part of the telescope remained incomplete. Now, I found the 

 great and small specula in their places, a finder of four inches aperture at- 

 tached, the circles divided, and the clock for driving the telescope en- 

 shrined in the pier. One thing was wanting, weather fit for trying its 

 power ; and during eighteen nights there was only one of even middling 

 goodness. That, however, was suflacient to prove that the instrument is 

 thoroughly up to its intended work. I examined several nebulae and 

 clusters, with whose appearance in Lord Rosse's six-feet reflector I am 

 familiar, and the difference was far less than I expected. I may specify 

 among them 51 Messier, whose spirals were seen on strong aurora, and the 

 nebula in Aquarius, with its appendages like the ring of Saturn. Its defi- 

 nition of stars is very good : a Lyrse had as small and sharp an image as I 

 ever saw on such a night ; and a few pretty close double stars were well 

 and clearly separated. Part of this is probably due to the lattice-tube, 

 which permits the escape of heated air, but more to the figure of the sj)e- 

 culum, which is truly parabolic. The peculiar nature of the mounting 

 brings the circles completely within reach of the observer's assistant ; and 

 the mechanical appliances for the motions in right ascension and polar 

 distance are so perfect, that we set the instrument on the faint objects which 

 we were examining with great facility and rapidity. One man can reverse 

 the telescope in a minute and a quarter ; the quick motion in polar distance 

 is of course far easier, and the slow one acts more like the tangent screw of 



