1819.]  Delcros on the Influence of the Time of Day, &e. 197 
ArTIcLE VI. 
Examination of the Influence of the Time of the Day upon Baro- 
metrical Measurements. Extracted from the Researches of 
M. Delcros.* 
M. Detcros undertook to resolve this problem: ‘‘ Suppose, 
two barometers, separated from each other by a certain space, 
both horizontal and vertical; at what time of the day ought they 
to be observed, that the height of the stations resulting from 
calculation may approach the nearest to accuracy?” 
To obtain the solution, M. Delcros made choice of two sta- 
tions, conveniently situated for observing at the same time two 
barometers, well constructed, at five different periods of the day, 
each separated from the other by an interval of two hours; 
namely, at eight o’clock in the morning, ten o’clock, noon, two 
o’clock, and four o’clock in the evening. One of the stations was 
at Strasburg, in the cabinet of M. Herrenschneider, Professor of 
Natural Philosophy in the Academy, and a very accurate 
observer. The other station was the castle of Lichtemberg, upon 
an insulated summit of the Vosges, about ten leagues north from 
Strasburg, and about 264-35 metres above that city, and con- 
nected with it by one of the triangles belonging to the great base 
of Ensisheim. Colonel Henry, who had the superintendence of 
the geodesical observations executing in the east of France, had 
resolved to make a set of astronomical observations at Lichtem- 
berg, to determine the amplitude of the celestial arc of the 
meridian from Geneva to Luisberg, an are which this point divides 
into two parts nearly equal. M. Delcros being obliged to make 
a considerable abode at Lichtemberg, in order to assist bis 
superior, took advantage of the opportunity to make a complete 
series of barometrical observations in the same place at the five 
times of the day above-mentioned. These observations were 
simultaneous with others made at Strasburg by Professor Herren- 
schneider. They were continued for 22 days, which gives 100 
observations to. compare, disposing them in five groupes. of 
corresponding observations, which ‘“‘ may be compared with each 
other. .This comparison has been carefully made by M. Delcros, 
which, in his opinion, may add some rays to the luminous pencil 
collected by the celebrated philosopher Ramond, to whom the 
barometrical method is indebted for so many labours—for so 
many profound investigations—for so many precious memoirs, in 
which he has united the principles of a simple and luminous 
philosophy with the charms of style.” —— 
These observations have been arranged by the author in two 
very interesting tables. 
* Translated from the Bibliotheque Universelle, vii. 236. (April, 1818.) 
