162 ANNUAL KECORD OF SCIENCE AND INDUSTRY. 



tained during the war. The recent publication of a memoir 

 by an Italian on this same subject has led the members of 

 the French Commission to state that the Italian method of 

 observation and their results, as announced by them, offer a 

 very complete analogy with those of the French Commission ; 

 and, in order to secure priority, the latter body has made 

 public some of their results. The sealed packet was, there- 

 fore, opened by the Secretary of the Academy of Sciences on 

 the Yth of July, 1873, and from its contents we make the fol- 

 lowino; abstract : 



The apparatus used by the French Commission consisted 

 of two telescopes, one at each station, the stations being gen- 

 erally, of course, upon mountain -tops or other prominent 

 points. The telescopes were pointed directly npon each 

 other, so that a light placed at the focus of one was seen by 

 an observer at the eye-piece of the other. The brightness of 

 the image perceived by the observer would, of course, depend 

 on the intensity of the original light, the distance between 

 the telescopes, the apertures of the telescopes, and the state 

 of the atmosphere. Numerous experiments were made in 

 September, October, and November, 1870, in order to deter- 

 mine the best conditions of construction and establishment 

 of the apparatus. The signals were made simply by display- 

 ing and concealing the light, a conventional alphabet being 

 employed, probably not dissimilar to that known as the Morse 

 alphabet employed by telegraphers. The rapidity with which 

 signals were exchanged appears to have coincided very nearly 

 with the rapidity attained in ordinary telegraphy. The max- 

 imum distance between which signals were successfully ex- 

 changed appears to have amounted to thirteen miles. The 

 Commission also undertook to put Paris in communication 

 with the provinces by sending up two of its members in a 

 balloon, in order, if possible, to communicate their conven- 

 tional system of optical signals to those dwelling beyond the 

 lines of investment. The two members who undertook this 

 matter established themselves at Bordeaux, where they form- 

 ed a school of optical telegraphy, and were able to introduce 

 the use of non-achromatic telescopes of a very large size, a 

 step that was very advantageous in the matter of economy. 

 The first communication between Paris and the country be- 

 yond through the medium of these two branches of the Com- 



