G7S 



REPORT — 1900. 



The declinations in tlie early part of the series are eminently satisfactory; in 

 that part the motion was very small in S. Towards the end, when the comet was 

 moving quicker, the agreement is not so satisfactory. 



The right ascension varied most rapidly at the beginning of the series, and 

 the agreement would have been more satisfactory throughout, though more 

 noticeable at the beginning, if the epoch of observation had been some seconds 

 later. 



It is a very difficult matter to determine the proper time of exposure, since the 

 first few seconds in the photograph of a faint object do not seem to be used in the 

 blackening of the film. 



The importance of this point in the photographs of Eros recommended by the 

 International Oomite de la Carte du Ciel will not escape the attention of 

 astronomers. 



There is another point: how do these observations compare with those made 

 micrometrically in a typical observatory f To illustrate this I select that of 

 Strassburg, where the observations are of unusual excellence, and where the focal 

 length of the instrument is fairly comparable with that of the Greenwich tele- 

 scope. The series of Strassburg within tlie same dates, and over which the same 

 interpolation formula is available, is not quite so long, but fairly comparable. The 

 Greenwich places I'est in every case, it is believed, on the positions of three stars, 

 the Strassburg never on more than two, and sometimes on a single comparison. 

 The error in the star's place is therefore more effective. The errors are as 

 follows : — 



The probable error of a single observation here amounts to 



±2"'68and ± l"Ol 



which is less than that of the Greenwich observation in approximately the pro- 

 portion of 3 to 2. 



Pending further experiments, which I believe are to be carried out by photo- 

 graphic experts at the Paris Observatory, the importance of this comparison in 

 the matter of the Eros observations will not be left out of sight. 



5, On Needle-hole Maps for Meteor Observation. 

 By J. C. W. Herschel. 



1. For an original map the stars are plotted out on squared millimetre paper 

 to the scale of 1 dm = 45° by Professor Turner's formula,' primarily devised for the 

 p.'ates of the Astrographic Chart. 



As a check there is used 



^ cot (a - A) = sin P - 7) cos P.- 



2. The paper for the copies is sky-blue on one side and ^ivhite on the other, on 

 which the meteors' paths and descriptions are written. 



The needles used are the ordinary commercial needles Nos. 2-12 for magnitudes 

 1-5 to 4'0 by steps of quarter magnitudes. No. 12 is also used for all stars below 

 4-0, and an extra large needle for superior stars. The points are ground flat and 

 the needles set in handles. The holes made are round and clean. 



' Montlily Notices, R.A.S., 1894, vol. liv., November. 



= For a-A = 90°, when the formula is indeterminate, |= -°j'^. 



cos 1' 



