322 



Mr. W. Lassell on the Great Nebula in Orion, [Apr. 23, 



tangent to the path, becomes a measure of the time of flight, according to 

 the usual law of falling bodies ; and the mean horizontal velocity being 

 thus known for a series of different ranges, we can calculate the mean ve- 

 locity for every 100 yards of a long range, and thence determine the re- 

 sistance. 



The author commenced his calculations from an assumed velocity of 

 1360 feet per second, in accordance with the results obtained at short 

 ranges, and assumed for trial a resistance varying as the square of the 

 velocity, but found that this law did not fit the results at all. A resist- 

 ance varying as the cube of the velocity was then tried, and found very 

 nearly to agree with the results of observation ; and the agreement be- 

 came, we may say, perfect, when the assumed initial velocity was slightly 

 corrected. 



As the calculations and experiments were all made without any notion of 

 the resulting law, and without any knowledge of the work already done by 

 Professor Helie and Professor Bashforth, they aiford a remarkable confir- 

 mation of the results obtained by those gentlemen. This is the more 

 worthy of notice, as their data belong to pieces of large calibre, and the 

 author's to small arms. 



IV. Remarks on the Great Nebula in Orion.^^ In a Letter addressed 

 to Prof. G. G. Stokes, Sec. K.S. By W. Lassell, F.H.S. Re- 

 ceived February 28, 1868. 



I have been so much interested by the perusal of Lord Oxmantov.n's 

 observations and drawing of the Great Nebula in Orion, published in the 

 present volume of the * Transactions,' that I venture to offer you a fev/ 

 remarks upon them — the more readily, as I may be supposed to be some- 

 what familiar with that object, though observed with less advantage of 

 optical power. 



On comparing the present drawing with my own, made with the four- 

 feet equatorial during my late sojourn at Malta, I find that of the 93 nevv^ 

 stars in Lord Oxmantown's list, there are, I believe, only 24 within the 

 more limited area of my dramng. K good many of these have escaped 

 mv notice, while, on the other hand, I have detected several which I do 

 not find in the present Catalogue. The following are instances of a few : — 

 Three stars north-preceding No. 119; four stars about the hypothenuse 

 of the nearly right-angled triangle formed by the stars A7, 52, and 53 ; 

 two stars in the triangle formed by 30, 32, and 35 ; a dehcate point about 

 20" from 104, with several others. Some of these I have so repeatedly 

 and certainly seen, that I wonder not to find them here. The explanation 

 of this discrepancy may possibly in some instances be found in variabihty, 

 but must, I think, be rather sought for in the influence which the state of 

 atmosphere has on such delicate objects, when the highest combinations of 

 -light and power are brought to bear upon them. As this is a nebula of 



