On the Eclipses of Jupiter’s Satellites. 265 
copper flask containing a horizontal stirrer or agitator, which 
being kept in motion by means of a handle rising above the flask, 
prevented the caoutchouc from burning to the bottom. 
I am, dear sir, yours, 
A. AIKIN. 
P.S.—In the preceding notice I have stated the method of 
applying the caoutchouc precisely as I have myself practised it, 
and as I communicated it to Mr. Perkins*. To him is owing 
the suggestion of incorporating the caoutchouc with oil of tur- 
pentine; which makes it more easy in its application; and has 
the further advantage of causing the caoutchouc to dry into a 
firm tough varnish, impenetrable to moisture, and capable at any 
time of being removed by means of a soft brush charged with 
warm oil of turpentine. 
T. Gill, Esq. 
* Mr. Perkins employs the caoutchouc in preserving his engraved steel 
blocks, plates, rolls, dies, &c. from oxidation. 
LIX. On the Eclipses of Jupiter’s Satellites during the pre- 
sent Year*, 
Tu 1s Table contains a list of all the Eclipses of Jupiter’s sa- 
tellites, marked as visible at Greenwich, deduced from the Con- 
naissance des Tems for 1822, by deducting the difference of the 
meridians, or, 9’ 21”. The times of the eclipses, in that work, 
have been computed from M. Delambre’s mew tables published 
in 1817+. I have calculated several of them, and find them 
correct. I know not from what tables those in the Nautical 
Almanac have been computed (the laudable custom of informing 
the public on these points having been for some years omitted), 
but there is so striking a difference between the results in the 
two works, that I thought it might be acceptable to the practical 
astronomer to have them presented at one view. The differences 
amount, in some cases, to 2’ 10”. If the computations in the 
Nautical Almanac have been made (as formerly) by to separate 
ersons, and should prove incorrect, it is singular they should 
both have fallen into precisely the same errors. The list con- 
tains only those eclipses which are recorded in both works. The 
_last column may be useful to the observer when looking out for 
* From Mr. F. Baily’s “ Astronomical Tables and Remarks for the year 
1822 :” a work printed for private circulation only. 
+ The Commissioners of the Board of Longitude have deferred the use 
of these tables till the year 1824; a period of seven years from the date 
of their publication. This is nearly fulfilling the injunction of Horace : 
nonumque prematur in annum. It certainly gives ample time for the detec- 
tion of any errors. 
Vol, 59, No, 288, April 1822. L 1 an 
