The Earl of Rosse on the Nebula. 237 



in the pressure of the supporting medium depends chiefly, if not en- 

 tirely, upon the ready access of atmospheric oxygen to, or its com- 

 parative exclusion from, the interior of the flame. 



5. Down to a certain minimum limit, the more rarefied the atmo- 

 sphere in which flame burns, the more complete is its combustion. 



" On the Anatomy and Physiology of the Spongiadae." Part II. 

 By J. S. Bowerbank, LL.D., F.R.S., F.L.S. &c. 



"Further Observations upon the Nebulae, with practical details 

 relating to the construction of large Telescopes." By the Earl of 

 Rosse, F.R.S. 



In this paper the processes which were found best to answer in 

 casting specula of 6-feet aperture have been described at some length ; 

 and the precautions which were taken to prevent accidents during 

 the progressive stages of manufacture. 



Some information, which may perhaps be useful, has also been 

 gathered from the memoranda kept on each occasion when the spe- 

 cula were ground and polished ; and the results of a long experience 

 in the different manipulations have been put together in a practical 

 form, so as best to enable the civil engineer to undertake the con- 

 struction of large telescopes as a matter of business. 



A few hints have been given on figuring and repolishing large sur- 

 faces, which the astronomer may find useful should his services be 

 required in distant countries. 



An attempt has been made to define the extreme limits to which 

 telescopic vision may be pushed in this country, in answer to the 

 question whether instruments of greater dimensions might not be 

 advantageously constructed. 



The peculiarities in the mounting of the large telescope are slightly 

 noticed, and their advantages and disadvantages explained, as they 

 have been brought out by experience. 



This is followed by a selection from the observations made during 

 a period of six years, accompanied by drawings of the more remark- 

 able objects. 



The principal results seem to be a large addition to the list of ne- 

 bulae with curved or spiral branches, and many new double and 

 multiple nebulae. A variety of objects have been also pointed out 

 upon which the labour of a careful scrutiny will probably be amply 

 repaid, with a similar instrument, even in this climate. A still larger 

 number have been marked off, which to save time may be passed 

 by, unless some new views on Cosmogony should suggest sufficient 

 motives for rcobserving them. A record has been made, which, to 

 some extent, will be available hereafter for comparison with the 

 heavens, and a few cases of suspected change have been noticed, 

 where the evidence, however, is by no means conclusive, 



"Observations on the Posterior Lobes of the Cerebrum of the 

 Quadrumana, with a Description of the Brain of a Galago." By 

 'William II. Flower, Esq. 



