PHILOSOPHICAL TRANSACTIONS. 
I. Researches on Solar Physics. Heliographical Positions and Areas of Sun-spots 
observed with the Kew Photoheliograph during the years 1862 and 1863. By 
Warren De La Rue, Esq., Ph.l ?., F.R.S., F.R.A.S., Pres. C.S., Balfour Stewart, 
Fsq., LL.B ., F.R.S . , F.R.A.S., Superintendent of the Kew Observatory , and Benjamin 
Loewt, Fsq., F.R.A.S. 
Received March 31, — Read April 30, 1868. 
1. We have been hitherto engaged in preliminary researches devoted chiefly to the 
physical nature of the sun, but we now propose to give a first instalment of the mea- 
surements made with a view of making the solar photographs taken at Kew the basis 
of a new determination of the sun’s astronomical elements. Accordingly the present 
paper contains the results of measurements of the Kew sun-pictures for 1862 and 1863, 
i. e. the heliographical longitudes and latitudes of all spots observed in these two years, 
together with a full description of the methods pursued in the reductions. The results 
of the succeeding years, and their final discussion with reference to the sun’s elements, 
will be published hereafter. 
In addition to those measurements which have reference to the heliographical position 
of each spot, we have also measured the area of each group on each occasion when it 
was observed ; and we conceive that in thus giving the position and area of each group 
we give all the information regarding sun-spots that is capable of accurate numerical 
expression, at least in the present stage of our knowledge. 
Measurements made with the view of determining the Heliographical Latitude and 
Longitude of Spots. 
2. We need not again describe the measuring-apparatus and its various adjustments; 
for these have been already described by Mr. De La Rue in the Bakerian Lecture for 
1862. 
Suffice it to say that, in the photoheliograph by which the sun-pictures are taken, 
there is at the joint focus of the object-glass and eye-glass a system of two fixed wires, 
MDCCCLXIX. B 
