1807.) 
servatory, afford nearly similar results, 
while the same observations of M. Bou- 
vard, compared with those of M. Ray- 
mond, made at Marli-la-ville, indicate 
from one day to another differences from 
from ten to eleven metres in the relative 
height of the two stations; from which 
we may conclude, that the use of the ba- 
rometer, for measuring heights at a short 
distance, is not so certain as when the 
two stations are at a greater distance 
from ¢ach other. ‘The influence of me- 
teors always tend to diminish the appa- 
rent height, and observations made dur- 
ing a storm are never to be depended on, 
From all these considerations, it follows, 
that, in order to obtain the exact height 
of 2 mountain, it is not sufficient to take 
indifferently a medium between observa. 
tions made at different times and in dif- 
ferent seasons, as such a_ proceeding 
would evidently expose us to error. 
We shall not at present attempt to 
give any account, proceeds M. Delambre, 
of the large and extensive work which 
Messrs. Biot and Arago have nearly 
brought to a conclusion, since M. Biot 
has himselfread an extract from it during 
the present sitting. There was also 
read during the same sitting, 2 Memoir 
by Count Rumford, On the Adhesion of 
the Molecules of Water. But the re- 
porter only notices the principal results 
of the experiments made by this learned 
philanthropist upon the dispersion of’ the 
hight of lamps, by means of screens and 
globes of ground gluss. 
The facility with which we distin- 
guish objects, does not depend solely 
on the intensity of the heht, by which 
they are viewed, but likewise upon the 
shades; if they are simple and well de- 
fined, the vision is distinct; but, on the 
contrary, if the light arrive from several 
sides at once, there will be several 
shades which confound and enteeble the 
light, so that we see indistinctly, however 
great may be its brilliancy. A proper 
distribution of light is therefore not only 
important in point of economy, but also 
for the preservation of the eyes. 
The direct rays of a lamp from a dou- 
ble current of air fatigues the eye; and 
Count Rumford proposes, with a view of 
remedying this iaconvenience, the adop- 
tion of ditferent kinds of screens, and the 
employment of ground glass globes, 
What renders the use of these globes less 
common is the prevalent opinion that, 
in this way, a great portion of the light is 
Jost No person has hitherto, M, De- 
Proceedings of Learned Societies, 
175 
lambre observes, at least in France, en 
deavoured to remove this prejudice. 
Count Rumford, however, demonstrates 
by an experiment, simple and easy to. be 
repeated, that the loss is absolutely tri- 
fliog. he surface of the ground glass 
being fullof furrows and asperities, pre- 
sents to the hght numerous smooth 
planes differently inched, which disperse 
the light, render it milder, and distribute 
it in such a manner that it fails more 
uniformly on every part of the object 
we wish to enlighten 
This advantage is not the only one 
derived from the employment of ground 
glass. According to Count Rumford, by 
its substitution for polished glass in our 
windows, the light would be more equally 
diffused m all the apartments, from the 
top to the bottom of the building. This 
would prove particularly useful in large 
cities, where the narrowness of the streets, 
and the height of the houses, prevent the 
hight from entering, except in an oblique 
direction. 
The Memoir is concluded by the de- 
scription of a lamp, which is so con- 
structed that we do not perceive any 
direct rays, while it sheds a mild and 
equal light over every part of a large 
hall, without leaving any of it in shade, 
though the reservoir containing the oil be 
circular, and the cylinders which disperse 
the light, be placed in the center, 
When treating of this invention, M. 
Delambre justly observes, that what ren- 
ders all the researches of Count Rumford 
particularly valuable, independently of 
the accuracy of his experiments, and the’ 
profound knowledge which he displays, is, 
that his labours are directed towards ob- 
jects of public utility. Weshould givea 
very lmperfect idea of the labours of this 
class, continues the reporter, were we to 
omit noticing those works which have 
been produced by the ditferent members 
in the course of the present year. Some 
of our sittings, he continues, are dedi- 
cated to receiving the memoirs of those 
learned men, who have not yet been re~ 
ceived as members of the Institute, and 
ainong whom we contemplate with sa- 
tisfaction many, who will one day add te 
its celebrity, and-extend the boundaries 
ofscience, ‘Lhe reports of the commis 
sioners appointed to examine their works, 
or the inventions respecting which the 
government have required the opinion of 
the class, are themselves frequently very 
unportant memouirs,in which are displayed 
equal impartiality.and erudition, in dis- 
cussing 
