1870.] 



Great Melbourne Telescope, 



221 



effort, I have been unable to catch them ; the borders, however, stretching 

 to the stars, as in the figure, are occasionally pretty well seen. On one or 

 two occasions I have suspected the existence of a link between the nebu- 

 losity about the star No. 10 and the lower portion of the ft; this, however, 

 requires verification. 



At the f. end the upper and smaller semicircle is plainly marked, the 

 lower and larger very faint, and consequently its exact figure uncertain ; 

 there is certainly some very faint nebulosity leading through the groups of 

 stars north of the three bright f. end stars, but it has not been added to 

 the sketch on account of its uncertain figure and extreme faintness. 



3570. A small but beautiful spiral. The two brighter knots are re- 

 solvable ; the greater brightness of these knots is not particularly shown 

 in Sir John Herschel's sketch (Plate I.), but is mentioned in the observa- 

 tions ; the general ground is only slightly nebulous. 



Of work out of the regular course, amongst other things, Neptune has 

 been observed on some five or six occasions for figure and a second satellite, 

 with only negative results. 



In the absence of a photographic apparatus to be used at the uninter- 

 rupted focus of large mirror, attempts have been made to utilize the 2nd 

 or Cassegrain image ; an average exposure of near ten minutes on an eight- 

 day moon produced pictures which (by no means good) were of sufficient 

 promise to make it worth while to resume the attempt under more 

 favourable conditions. 



The time of exposure is somewhat surprising, and would seem to accuse 

 a great loss of chemical rays by a second perpendicular reflexion ; but 

 perhaps the more legitimate conclusion would be that the inactivity was 

 mainly due to absorption at the surface of the large mirror, which was 

 then very yellow. 



The spectroscope arrived some time ago, but has not been much used ; 

 it is thought that for star work of any value some modification will be 

 required, principally the exchange of the present collimator for one of 

 longer focal length. A greater dispersion, moreover, seems desirable ; for 

 nebular work, however, for which it was mainly designed, the spectroscope 

 in its present form, which is handy and compact, will be of much service. 



For spectroscopic work on objects having a sensible diameter, the great 

 telescope itself labours under some disadvantages ; the enormous focal length 

 and consequent magnification of the image is a serious inconvenience in 

 the case of faint objects, and may be only partially remedied by a suitable 

 condenser. This magnifying of the image may, however, in some cases be 

 advantageous : I allude to the possibility thereby afforded of viewing small 

 definite portions of moderately bright objects ; unfortunately the objects 

 with which we have to deal are seldom of such a character. 



Of nebulae, Orion has been examined for purpose of practice. The three 

 lines are plainly and conspicuously seen ; the hydrogen line is compara- 

 tively much fainter than I ha4 anticipated, and disappears in the fainter 



