MASKELYNE. 
474 
formance in 1792, calls it “ le recueil le plus precieux 
qtte nous'ayons.” Since that period they have been con- 
fiderably improved, and are univerfally allowed to po fiefs 
an unrivalled degree of accuracy. His catalogue of the 
right afcenfions and declinations of thirty-fix principal 
fixed ftars, with tables for their correction, is a mod ufe- 
ful and important performance, and is adopted in all ob¬ 
servatories. It is moftly diltinguiflied by the appellation 
of “Dr. Mafkelyne’s thirty-fix Stars.” His obfervations 
alfo of the fun, moon, and planets, are equally elleemed, 
and have been made the bafis of the folar and lunar ta¬ 
bles lately computed in France according to the theory 
of M. Laplace ; and which are republifhed in profeffor 
"Vince’s Alhonomy, vol. iii. The folar tables were cal¬ 
culated by M. Delambre, and the lunar by M. Burg; co¬ 
pies of which were transmitted to Dr. Mafkelyne, by or¬ 
der of the French board of longitude, with a grateful 
acknowledgment of the important affiitance derived from 
las Greenwich obfervations. 
Mr. Delambre obferves, that, fince the eftablifhment of 
the board of longitude in France, the obfervatories of Pa¬ 
ris and of Greenwich are direCled nearly to the fame ob¬ 
jects; and, furnifhed with inftruments equally good, they 
produce annually collections of obfervations equally pre- 
cife, which would ferye mutually to verify one another 
if there were occafion. They ferve as a fuppiement to 
each other, when the clouds which cover one obfervatory 
do not extend likewife to the other. The communica¬ 
tions are continual, and the obligations reciprocal. If 
the French tables are founded in a great meafure upon 
the obfervations of the Englilli, on the other hand the 
calculations of the Englifli are founded upon the French 
tables. But the lateft tables have been verified by as 
many French as Englifh obfervations.” 
Dr. Mafkelyne no more quitted his obfervatory. In 
1769 he remained in it to obferve the tranfit of Venus, 
though only one phafe was vifible at Greenwich; but he 
drew up inftruftions for the aftronomers whom Great 
Britain fent to different countries. He collected their 
obfervations, and deduced from them the parallax of 
the fun, and its diftance from the earth. His refult was 
the fame as that to which Dufejour came by comparing 
the totality of the obfervations of the two tranfits of 
1761 and 1769. He made many of the molt interefling 
and mod difficult obfervations himfelf, as thofe of the 
moon.; but neceffarily confided to his alTiffant thofe 
which were more eafy and lefs efiential. He followed 
■with inflexible rigour the methods eltablifhed by his ce¬ 
lebrated predeceflor Bradley, whom he even furpafled in 
the exaCtnefs of his daily obfervations. He brought to 
perfection the method of Flam If eed, of determining at once 
the right afcenfions of ftars and of the fun. It may be 
faid of the Obfervations that he publiihed, that, if by any 
great revolution the fciences were completely loft, and 
this collection preferved, there would be found in it fufn- 
eient materials for rebuilding almoft the whole edifice of 
modern affronomy, which cannot be faid of any other 
collection ; becaule to the merit of an exaCtnefs which 
lias been feldom attained, and never furpafled, it adds 
the advantage of a long feries of obfervations. Its pre- 
cifion is fo great, that it is very improbable that much 
can be added to it. The obfervations are excellent for 
the time in which they were made, and this time is the 
period in which they approached the neareft to perfec¬ 
tion. They will only increafe in value as they jncreafe 
in age; which unfortunately is not true either with re- 
fpeCt to the obfervations of Tycho and Helvetius, or to 
thofe of Flamfteed and La Hire, w hich, when made, pof- 
fefled all the exaCtnefs of which any idea could be form¬ 
ed ; but which, though not far removed front the prefent 
age, never can enter into any companion with the ob. 
fervations of the great aftronomers of the 18th century. 
Dr. Mafkelyne correfponded with all the aftronomers 
of the world. To be convinced of it, we have only to 
.filtt o.ver the memoirs of philofophers of every nation 
which he prefented to the Royal Society. He himfelf did 
not publifh quite fo often as could have been wifhed ; 
but it is very difficult for an aftronomer, charged with 
the duty of obfervations to be repeated every day, and al- 
moft every moment, to undertake great theoretical re- 
fearches, which he is tinder the neceftity of interrupting 
almoft every inftant. The writings which he has left ar« 
remarkable for juft ideas and an enlightened criticifm. 
Such is a differtation on the equation of time, where he 
has pointed out, with the requifite delicacy, a miftake of 
La Caille, and another lefs important miftake of Laiande. 
Lalande received very well the lefton which he thus got; 
but Bernoulli having inferted, feven years after, a traddi¬ 
tion of Dr. Mafkelyne’s memoir in his Collection for AC- 
tronomers, one of Lalande’s pupils (ci’Agelet) took up 
the caufe of his mafter in a manner that might have pro» 
duced a coldnefs between the parties concerned. The 
quarrel, however, had no confequence; and the two af¬ 
tronomers correfponded as ufua!. 
Some doubts having been raifed refpeCting the difFa*>- 
er.ce in latitude and longitude between the onfervatone* 
of Paris and Greenwich, Dr. Mafkelyne, to whom the ob¬ 
fervations were fent, (bowed, with his ufual moderation, 
that the doubts were improper; but he did not oppofe 
the methods propofed to obviate them. It was upon this 
occafion that the Englifh, who had hitherto done nothin^- 
refpeCting the grand geographical operations in which the 
French had diltinguiflied themfelves, fignaiized themfelves 
in their turn by methods which furpafled every thing that 
had been hitherto done. It was then likewife that°MM. 
Caflini and Legendre made the firft trial of the circle of 
Borda. Bouguer, at the end of his meafure of a degree 
in Peru, had endeavoured to determine the attraction of 
mountains, and the quantity which they draw the plumb- 
line of the feclor from the perpendicular direction. He 
had found a real and indifputable attraction ; but one- 
half lefs than ought to have refulted from the'fize of the 
mountain. Hence, he concluded that it was hollow with¬ 
in, and undermined by a volcano. Doubts might he en¬ 
tertained of a refult obtained by means of inftruments of 
middling goodnefs. Bouguer had himfelf expreffed a 
wifh that the experiment were undertaken in Europe 
with more care and with better inftruments. Dr. Mafke- 
lyne undertook this inquiry,, with the feCtor that he had. 
■with him at St. Helena, after having corrected the fuf- 
penfion, and altered the divifion. He made choice of 
Schehallien, a mountain in Scotland. It will be necef- 
fiiry to confult his memoir, in order to fee the care and 
the pains which this operation coft him which appears fo 
eafy. But it muff be obfervtd, that the laborious parts 
of the calculation, from Malkeiyne’s data, were com¬ 
pleted by Dr. Hutton, then a very young man; and for 
which the Royal Society voted him a gratuity of 250I. 
From thefe obfervations and calculations it appears, that 
the mean denfity of the earth is to that of water as 9 to 
2, and to that of (tone as 9 to 5; whence it is prefumed 
that the internal parts contain Jonte large quantities of 
metals. 
In 1792, Dr. Mafkelyne publiihed Mr. Michael Tay¬ 
lor’s Tables of Logarithms, a.laborious work, and an un¬ 
common monument of perfevering induftry. Theauthor 
had been encouraged by the doctor in the execution of 
it; and, having died when only a few pages remained un- 
finifhed, Dr. Mafkelyne brought it to a conclufion, and 
prefixed to it a very mafterly introduction, containing 
precepts for the ufe of it. Dr. Mafkelyne is faid to have 
been the inventor of the prifmatic micrometer; at any 
rate, the idea of employing a double refraction belongs 
to him, and Bofcovich acknowledges it. As he fet a 
high value on the excellent inftrument* which he ufed, 
he did his utmoft to preferve and improve them, by mak¬ 
ing fuch additions as his experience and (kill in op¬ 
tics fuggefied. He found the inconvenience of narrow 
openings, then ufed in all obfervatories, and therefore he 
had thofe of Greenwich enlarged. It had been lately 
fufpe&ed 
