58 
On the Long itude of Dili 11. 
[Feb 
those made under another wellknown meridian, which, as far at least as observations 
in Europe are concerned, are seldom accessible for years after they have been 
made. 
We hope that those of our readers who have it in their power will comply with 
the request made by the writer of the following letter, to communicate any corre- 
sponding observations made in India : — 
To the Editor of Gleanings in Science. 
Sir, 
I do myself the pleasure of sending for insertion in your valuable Gleanings, an 
abstract of some observations of lunar transits and occultations of stars, made 
with the view of determining the longitude of Dildi. 
The lunar transits were all observed at Gurglon, which has been determined 
by survey to be 48 seconds of time, west of the Jama Mesj'ul at Dihli. The in- 
strument is a most excellent one for its size, made to my particular order, by Dol- 
lond, of 30 inches focal length, and the power I have always used is 60, which it 
bears remarkably well. My chronometer is an eight-day one, by Barraud, and 
although not perhaps quite equal to those made now-a-days, yet as the time has 
always been determined by Stars culminating at no very great intervals from the 
Moon, I consider it may well be depended on. 
I shall feel much obliged to any of your Astronomical friends who will furnish 
corresponding observations of any of the lunar transits, noting the time of pas- 
sage of any stars not differing in declination from the Moon more than 10° or 
15° : I shall then give mine also for such particular periods. 
It may well be supposed, that my calculations are not free from errors ; I have, 
therefore, given the means of detecting them, should any person feel disposed (as 
I hope some one may) to recalculate the observations. The sidereal time of the 
passage of the Moon’s limb over the meridian is all that is required ; if it be taken 
for granted, that I am right thus far, (and I am prepared to furnish all particulars, 
if called upon to do so,) I cannot perceive how the results should be otherwise 
than correct. Regarding the time, I have been very minute and particular, 
and I do not think I can have committed any error here ; but for the rest of the 
calculations I do confess that I have not always had quite so much patience as they 
require. To prevent any misconception regarding the dates where the Moon’s 
second limb is concerned, it may be as well to say, that I use the common civil 
reckoning as to the day of the month : for instance, the transit of the Moon’s second 
limb, on Dec. 17th, 1829, was observed on the morning of the 17th, before noon, 
therefore, on the 16th, astronomically speaking. 
The occultations were observed at various places within about 50 or 60 miles from 
Dihli, and the results reduced to the Jama Mesjid ; the differences of longitude 
being deduced from the survey I was then conducting. The greater part of these 
observations having been made in camp, where I could not have the advantage of 
a transit instrument for determining the time, I was obliged to have recourse to 
equal altitudes of the Sun, and as I could not always get these on the day immedi- 
ately before and after the occultation, the rate of the chronometer has sometimes 
been depended on rather more than could be wished. The results, however, (with 
only two exceptions, marked doubtful in the list, and which I should be inclined 
to reject only that I think it the fairest way to give all the observations,) will, I hope, 
be tound to agree as closely as could be expected. 
“ T har <“y be necessity, I should suppose, to enter into any detail of the 
method of calculation I have adopted in my transit observations or occultations; 
a ““' d J 0 "’ "V? of , >’ our “■'respondents wish it, I shall be happy to send 
5 a Type du Calcul of each sort, complete in all the details. 
% 
