171 
Alexander S. Herschel, Esq., to li. P. Greg , Esq. 
Collingwood, Hawkhurst, Kent, 
1865, April 11. 
£< I was much obliged by the receipt of an observation of 
the auroral arch of March 20 (from the Liverpool Mercury), 
as seen at Windermere. Compared with another letter from 
the same writer (Mr. Hall) in the Standard, it gave a good 
place by the stars. In the ‘ Proceedings of the Manchester 
Literary and Philosophical Society’ is another description by 
Mr. Baxendell. The arch was well observed here, almost 
stationary, varying its altitude from 18° to 20°, and at last to 
22° or 23° in the course of half an hour. The first observa- 
tions correspond with those of Windermere, at the time when 
the arch was nearly vertical over Windermere; and the last 
with those at Manchester when the arch, as seen by Mr. 
Baxendell, was nearly overhead at Manchester. Both give 
the height of the arch 102 miles above the earth, and I 
doubt if a better double observation of an arch of the aurora 
of the ‘ skipping-rope ’ form has ever been obtained. The 
result can hardly be more than five miles, certainly not so 
much as ten miles in error either way. Mr. Airy says that 
among twenty to fifty auroras that he has witnessed he has 
only twice seen the auroral arch, ‘ rising like a skipping-rope.’ 
Perhaps you would have the goodness to communicate Mr. 
Airy’s letter to Dr. Joule, as it will interest him in his 
observations of the magnetic variations ; and at the same time 
to Mr. Baxendell.” 
The Rev. T. P. Kirkman, F.R.S., made the following 
communication : — 
As the printing of my completion of the Theory of Groups is 
delayed longer than I expected, I desire to insert the following 
table of corrections to be made in the list of titles at page 142 of 
the Proceedings of this Society, July, 1863. 
b 
