TRMSACtlOJJS OF SECTION A. 



677 



It wag found that during the two and a half hours' difference of time 

 between the times of totality the main prominences had changed considerably 

 in shape and form, but the polar rifts at the north polar region did not undergo 

 any alteration. 



The comparison has further led the author to advocate the employment of 

 long-focus cameras for such eclipse work, and to eliminate the necessity of 

 enlargement afterwards. 



An explanation is also given to account for the extreme sharpness of the 

 lunar limb on one of the long-exposure photographs, the chief argument employed 

 being the very rapid diminution of intensity of the corona as the outer layers 

 are reached. 



Dsscription of the Neiu PlbotographiG Equatorial of the Cambridge 

 Observatory. By A. R. Hinks, M.A. 



3. Diagram for Planning Observations of Eros at the Opposition of 

 1900-1. By A. E. Hinks, 31. A. 



4. On some Points in connection tvith the Photography of a 

 Moving Object. By W. E. Plummer. 



I have recently had occasion to make some investigations in connection with 

 the theory of Comet 1899, I. The object of the present paper is not to call 

 attention to the form of the orbit, so that that point need not be considered. 



But in the course of the examination of the observations I was led to com- 

 pare a series of places .of the comiit obtained under the superintendence of the 

 Astronomer Royal, by means of photography with the Thompson Equatorial. 



There is, so far as I know, no series of equal length in which the places of a 

 moving object have been determined by photography, and it seemed desirable to 

 investigate the peculiarities with some care. 



The series extends from May 'lo to June 10, 1899, during which time the 

 comet passed over some 80° of R.A. and 30° of declination. 



It is not usual to compare the final elements with individual observations, but 

 only with the normal plnces. The photographed places have therefore been com- 

 pared with the preliminary orbit, in this case an hyperbola : and the small deviations, 

 which are removed by the solution of the Equations of Condition, are displayed in 

 the comparison. 



But for the purposes of the present investigation it is sufficient to remove 

 these discrepancies by any convenient interpolation formula, and so obtain the 

 deviations of the observations from the true path of the comet. 



When this is effected the following deviations are noticeable : — 



da cos S 



f/S 



1899 



da cos 5 



dS 



The probable error of a single observation, derived simply from the disagreement 

 from the mean, is, in the case of a, ± 4"-16, and in b, ± :2"-85. 



There seems no prima facie reason why the right ascension coordinate should 

 not be determined with the same accuracy as the declination if the epoch of 

 observation is successfully established. 



