ASTRONOMY OlST MONT BLANC. 185 



and had noted the absence of any oand or elongation between the 

 phinet and the hniar disk, which indicates the remarkable perfection 

 of the seeing. In this connection it shoidd be noticed that in lOO-t 

 M. Hansk}^ made an interesting observation of the zodiacal light from 

 Mont Blanc, when he perceived details very difficult to distinguish 

 under any ordinary conditions. He has also attempted to photo- 

 graph the solar corona, but the results have not been satisfactory, and 

 will be repeated. 



Messrs. Fery and Millochau have undertaken to determine the 

 distribution of radiation over the solar disk, employing Ferj^'s pyro- 

 metric telescoi:)e. This comprises a tube of variable aperture con- 

 taining a silvered glass concave mirror; a thermoelectric couple 

 in the focus connected with a galvanometer, and a prism which 

 reflects a beam for guiding. Observations Avere made on Mont Blanc 

 and at Chamonix and Meudon. 



These examples will suffice to show that the observatory perched 

 on the heights of Mont Blanc otl^'ers facilities to astronomers for 

 the prosecution of a variety of special researches of great delicacy. 

 But the scope of observations has little by little expanded, so as to 

 comprise also meteorolog}" and physiology. The work has usually 

 to be carried on in the summer months, however, for the winters 

 are apt to be too rigorous. In 1901 ]M. Xordmann found recorded 

 by a Tonnelot minimum thermometer a temperature of — 45° C. 



Among experiments of other kinds Avhich have been made in the 

 past few years may be cited as particularly important some which 

 were carried on in 1899 and 1900, with the support of the admin- 

 stration of the telegraph, to determine the insulating properties of 

 ice. Bare wires of galvanized iron were laid upon the glacier at 

 some meters apart. The experiments were commenced by Messrs. 

 Cauro and Lespieau, and continued by Lespieau alone after the 

 fatal accident of Cauro, who met with a terrible fall in a trail on 

 the mountain of la Cote. The experiments showed that a telegraphic 

 line of great length, such as 100 kilometers, for example, may be 

 established with bare wire upon glaciers, and give good service. 

 This result is of value for telegraphy on the high mountains, 

 although there had been before trials of short lines laid on snow. 



M. Maurice de Thierry made in 1894 and 1899 a series of determi- 

 nations of the atmospheric ozone, ammonia, and carbonic-acid gas at 

 different altitudes. M. Le Cadet, in 1902, studied the atmospheric 

 electricity from the summit of Mont Blanc. M. Nordmann also tried 

 to detect electromagnetic waves emanating from the sun, but with 

 negative results. Of another nature are the spectroscopic studies of 

 the blood commenced by Doctor Henocque in 1902, and continued 

 after his death by M. Raoul Bayeux ; the observations of Messrs. 



