336 MR WILLIAM SWAN ON THE 
protracted on. a trustworthy map of the environs of Goteborg,* are very well 
satisfied by a point, which, from the known latitude and longitude of the Observa- 
tory, I find to be in latitude 57° 42’ 57’:3 N. and longitude 0° 47™ 45*2 E.+ 
So many phenomena occur at the total phase of a solar eclipse, that I wished 
to avoid having my attention distracted by my being obliged to count the beats 
of the chronometer in taking observations for time. I therefore gladly availed 
myself of the assistance of Mr Epwarp W. Lang, Advocate, of Edinburgh, who 
kindly undertook to read the chronometer, and mark the times at a preconcerted 
signal. His co-operation proved quite invaluable; and it is with the greatest 
pleasure I avail myself of this opportunity of acknowledging my obligations to 
him. 
The telescope I employed in observing the eclipse was furnished by Mr Apre. 
It has avery good object-glasst of about 2°3 inches aperture, and 31-5 inches focal 
length, and was mounted on a rough equatorial stand. Of the eye-pieces be- 
longing to this instrument, I chose that of the lowest power, magnifying 28 
times, as it was necessary for some of the observations I purposed to make, to 
have the entire disc of the sun within the field of view at once. I also then 
thought, and I am still of the same opinion, that any advantage gained by using 
a higher power would be more than counterbalanced by the time lost, during the 
short duration of the total phase of the eclipse, in directing the telescope from 
point to point of the moon’s limb, instead of seeing the whole at once. In effect, 
the power I had chosen proved very convenient, and apparently quite sufficient 
for observing the interesting phenomena of the total phase; while the definition 
of the corona and the red prominences seemed as perfect as could be wished. 
I had prepared some slips of smoked plate-glass, gradually increasing in depth 
of tint from one end to the other, for the purpose of observing the sun before the 
period of total obscuration; but Professor Curvanurer kindly lent me a dark 
glass, by TRoucHton and Simms, consisting of wedges of coloured glass achroma- 
tised by a colourless prism.) This combination of glasses made the sun appear 
yellow, slightly tinged with green, and I willingly adopted it in preference to 
the smoked glasses, as the definition of the sun was decidedly sharper when it 
was used instead of them. This dark glass slid in a groove in front of the eye- 
piece, so as to admit of being instantly removed. 
From the conflicting accounts which were given regarding the red prominences 
* This map, published by A. Hanr, is entitled Topografisk Karta éfuer Gétheborgs Omgifning 
Jemte plan éfver Staden med dess nya Hambyggnad, 1844. 
+ Since this paper was read, Lieutenant Perrensson has kindly verified my calculation, and assigns, 
as the position of my station, lat. 57° 42’ 58”-0 N., long. 02 47™ 4553 E. 
t As the value of the following observations must depend greatly on the character of the instru- 
ment with which they were made, I may mention that this telescope shews bright stars, with per- 
fectly round, well-defined discs; and, with a power of 75, the two stars in Castor are seen com- 
pletely separated. 
§ To Professor Cuevantrer, and especially to Lieutenant Perrersson, my warmest thanks are 
also due, for their kind assistance and advice. 

