SS6 Account Ohservations made in France 
Board of Longitude to the Minister of Marine, that M. D’Assas 
was promoted from the rank of Capitaine de Fregat to that 
of Capitaine de Vaisseau.” 
M. D’Assas has been engaged for nearly ten years in his la- 
borious observations. The method he has adopted may be con- 
sidered entirely of his own invention ; for, although Galileo sug- 
gested something similar, it appears to have been wholly un- 
known to M. D’Assas, whose method is greatly preferable. 
M. D’Assas places an isosceles triangle ABC, Plate VII, 
Fig. 11., composed of three bars of iron, on a mountain, and 
observes, by means of a telescope placed in the meridian, be- 
tween 600 and TOO yards to the northward of the triangle, the 
occultations of a star at different seasons of the year, at the two 
equal sides of this triangle. The base of the triangle AC is fif- 
teen times its height BD. He observes, for instance, the occul- 
tations at w, and that at n. Now, if, after some months, 
the effect of parallax be to elevate the star 1" in altitude, the 
interval between the two occultations at m and n will be chan- 
ged 1" in time. Of course, the interval will also be changed from 
the changes of altitude, arising from variation of refraction, pre- 
cession, aberration, &c. &c. ; but these being known, may be 
allowed for. M. D’Assas seems well aware of the difficulties 
attendant on his method, and of the precautions necessary to be 
taken not to be deceived in his results. The greatest difficulty 
he feels he has to contend with is from uncertain refractions, as 
his observations must necessarily be made on low stars, although 
he has succeeded in observing stars above 30° high. He propo- 
ses to use six triangles instead of one, that the mean of the re- 
sults from the occultations on each day may be more exact. 
The report, after stating minutely the precautions taken by 
M. D’Assas, proceeds to give some of his results. The most 
remarkable and best founded of them appears to be from his 
observations of Keid, (40 d. Eridani, 5. Mag.) Bigel, and Si- 
rius. He also observed above 100 other stars ; and the num- 
ber of his observations exceed 4000, affording a wonderful ex- 
ample of labour and perseverance. Each of these observations 
required delicate and troublesome operations. 
To verify his results, he deduces from his observations the 
annual movements in declination. The great proper motion of 
