FRENCH OBSERVATIONS. 27 



Kaeintz carried on a good many scattered but instructive forest and 

 agricultural observations before the publication of bis meteorology in 

 1831-'34. In 1839-'40, Bravais at Bossekop, and Thomas at Kaaford, 

 botli in Lapland, took a long series of winter tree temperatures. Bra- 

 vais put the bulb of a mercurial thermometer in the heart of a liviug 

 pine wbicli was G inches in diameter. Thomas compared the temi)era- 

 tures of two large pines close together, one dead and the other living. 

 The latter showed a slightly higher temperature than the former. 



In the winter of lS57-'r)8, Bourgeau carried on a series of tree tem- 

 Xjerature observations at Fort Carlton, on the Saskatchewan Eiver, 

 latitude about 52°. 



FRANCE. 



The beginning, however, of systematic observations on the short- 

 range forest meteorological problem of the relative condition of the air 

 in and about forests and the incitement to the modern activity in this 

 direction seem to have come from the observations of M. A. C. Bec- 

 querel and his son Edmund, wliich began at Chatdlou-sur-Loing, about 

 70 miles south of Paris, on July 30, ISoS. These observations, now re- 

 lating to forest meteorology, now to some other branch of the science, 

 now carried on at Chatillon or its vicinity, now at Paris in the Jardin 

 des Plantes, and generally with the aid of the French Academy of Sci- 

 ences, have been conducted by MM. Becquerel and his son from that 

 time to a quite recent date, and are probably still continued. 



The memoirs and briefer communications which have been made to 

 the academy, based on these observations, form a large and highly in- 

 structive addition to knowledge in this science, and they have been 

 abundantly drawn on by subsequent writers. It is in some respects an 

 advantage, in others a disadvantage, that the Messrs. Becquerel have 

 used a special form of instrument in their observations and have fol- 

 lowed independent methods. The disadvantage lies in the fact that 

 this makes the observations not strictly comparable with those taken 

 at regular forest meteorological stations, and when the question is one 

 of relatively small dififerences, as that of temperatures and rainfall 

 within and without forests, this lackof comparability is a serious draw- 

 back. On tiie other hand, there is a great advantage in getting results 

 by difterent methods and with different instruments, for it serves to get 

 rid of errors that dejiend on the method. Conclusions drawn from two 

 entirely different sorts of observations are worthy of more confidence 

 than those drawn from two sets taken in the same way. 



The observations of the Messrs. Becquerel were taken with electric 

 thermometers. They depend on thermo-electric principles, and the 

 elder Becquerel had published studies on them as early as 182G, and 

 afterwards used them in determining the temperature of the different 

 envelopes of tlames. The instrument as used was composed of a closed 

 circuit a part of which was of copper and a part of iron. The two are 



