336 
LORD WROTTESLEY ON THE PERIODICAL OBSERVATION OF STARS 
vidual measures, or the weight of the set, has been divided by 10 prior to its entry in 
the subjoined tables ; while therefore the number 5 should express the weight of a 
set of average goodness, the number expressive of that weight is reduced in practice 
to 4. The measures when made are registered in the printed skeleton forms, origi- 
nally proposed by Sir John Herschel, and adopted, I believe, by almost all observers 
of double stars in this country. A number of these forms were bound together in a 
volume, and care was taken to fill up the different columns, so far at least as they 
refer to measures of position and distance. Whenever the weather permitted, a set 
of measures was obtained of each double star, on three separate days, at each period 
of the year marked out as the proper one for observation. The common arithmetical 
mean was used in taking the average of the partial measures, comprising each set, 
without taking the arbitrary weights into account. At the commencement of the 
series, the zero of the position circle was frequently determined ; but it was found to 
undergo no alteration that might not be attributed to error of observation ; from that 
time it became the practice to ascertain it about every two months ; but it was never 
found to vary more than about 2', a quantity very much within the error of observa- 
tion in determining an angle, as will appear in the sequel ; no zero was required for 
distance, as it was the practice to take an equal number of positive and negative 
readings. 
The observations were commenced on the 15th February 1843, and terminated the 
9th October 1849 ; and they were made almost exclusively by three gentlemen, who 
acted successively as my astronomical assistants, during the progress of the work. 
I have always found, that observations are better made when entrusted to one com- 
petent individual, who after a short time gains experience, and a facility of mani- 
pulation, which cannot be acquired by one who only occasionally observes ; and this 
uniformity in the mode of observing is particularly desirable, where the quantities to 
be determined depend on comparisons of observations made at different periods ; it 
was a subject of great regret to me, therefore, that I was compelled to make any 
change in the staff of my observatory during the course of this investigation, and I 
only observed myself on a few nights at the time of the first appointment of each 
assistant. 
Mr. Goddard observed from the commencement of the observations to October 2, 
1843; Mr. Simms from that time to the 11th of June 1844 ; and Mr. Philpott, ray 
present assistant, from thence to the conclusion. 
The results of the observations are embodied in five tables, and it now remains to 
explain the manner in which those tables have been formed. 
The First Table . — In the first table the stars are arranged in the order of their 
R.A.’s ; and the observations of each day, or sets, follow one another in the order of 
their date. 
An asterisk will be found attached to four of the stars in the list ; these are stars, 
which, on comparing their mean positions as ascertained in the course of this inquiry. 
