NOTES ON HALLEY'S COMET, 1910. 



By H. E. Wood, M.Sc, F.R.Met.S. 



A long series of photographs of Halley's Comet was obtained 

 with the Frankin-Adams Star Camera at the Transvaal Observa- 

 tory, during the m.onths of April, May and June, iqio.* They art 

 reproduced in Transvaal Observatory Circular No. 4, and a brief 

 description of them is given there. 



It is here intended to refer to a few points of general interest 

 which have arisen during the visit of the comet. As a wonderful 

 spectacle in the heavens, Halley's Comet much exceeded all expec- 

 tations ; at least to those who were situated in favourable latitudes 

 as we were in South Africa. 



On the morning of May 17th, the actual and unbroken length 

 of the comet's tail was found to be as much as 107 deg. On the 

 19th of May the head of the comet was not visible, but the end of 

 its tail was 150 deg. from the place of the head. There do not 

 appear to be any records of previous comets having tails of such 

 angular dimensions. The only comets having tails approaching 

 this size were those of 1618 and i86i (ii), but the length of the 

 tail of Halley's Comet far exceeded these. 



The head of the comet was very brilliant, but its brilliancy 

 appears to have been exaggerated in some quarters. It was not 

 as bright as the head of Comet 1910 a, as this could be seen quite 

 easily in full daylight, whereas Halley's Comet was never seen in 

 the daytime. It was probably just about as bright as Saturn but 

 not as bright as Venus. Although the tail of Halley's Comet did 

 not present such irregular features as did the tail of Morehouse's 

 Comet of 1908, yet there are many evidences of intense activity. 

 The photograph taken on April 21st shows the most irregular tail 

 of the Transvaal Observatory series of photographs. The appear- 

 ances shown on the photograph suggest changes of an explosive 

 character occurring near the head of the comet, followed by the 

 propulsion down the tail of huge volumes of luminous matter. It 

 has been shown by the examination of such irregularities, which 

 appear on photographs taken on consecutive nights that there is a 

 great increase of velocity as the matter recedes from the head. 

 Near the head the velocity of propulsion is of the order of five 

 kilometres per second, increasing to 90 kilometres per second near 

 the end of the tail.f 



Two photographs each of 31 minutes' exposure were obtained 

 at the Transvaal Observatory on the morning of May 9th. The 

 interval between the two photographs was only five minutes. A 



^Eighteen of these — direct contact copies on bromide paper, from 

 the original negatives — were exhibited when this paper was read at the 

 Cape Town Session of this Association, and are filed with the Associa- 

 tion's records. 



t Lick Observatory photographs. 



A 



