A. MATHEMATICS AND ASTRONOMY. 27 



are some fumaroles still active, but for some months most of 

 these have disappeared, and at present the vapor comes and 

 goes abundantly only from the base of the crater, where the 

 vertical depth is about seven hundred and fifty feet. The 

 instruments of the observatory on Mount Vesuvius, the 

 seismograph and the magnetic apparatus, after the violent 

 agitation that they experienced in the month of April last, 

 have little by little come to an absolute rest; but to-day 

 (early in July, 1873) they commence to be feebly agitated 

 in such a vray that the phenomena seem after a period of 

 degrees about to increase in intensity, but fire has not yet 

 appeared in the interior of the crater." " 



In remarking on the above, St. Claire Deville adds that, con- 

 forming to the thought that seems to inspire the last phrase 

 of the letter, he is disposed to admit that the approach- 

 ing period of activity that will probably be experienced 

 by the volcano will be that which he calls the "Strombo- 

 lian," and which consists in small eruptions, which will pro- 

 ceed from the centre of the crater at the summit of the 

 mountain. This will be a repetition of the phenomena of 

 July, 1856, one year after the great eruj^tion of 1855, and 

 which he was able to predict in advance. Monsieur Elie de 

 Beaumont observed that the labors of Deville have inaugu- 

 rated a new manner of studying volcanic j^henomena, and a 

 new special method of observing them ; they compare wor- 

 thily with those that Boussingault has so happily executed in 

 order to determine the volatile products of the great volca- 

 noes of the Andes, being himself inspired by the first trials, 

 made long ago by Sir Humphrey Davy. That vigilant ob- 

 server of Vesuvius, Palmieri, has also entered this path of re- 

 search, following Fouque in his researches on Etna, Santorin, 

 and the Caldeiras of the Azores, Avhose researches were lately 

 published in the Com2)tes Rendus^ in a memoir replete w^ith in- 

 terest. The employment of the spectroscope gives to the new 

 school of Vulcanologists an instrument the power of which 

 is equal to its delicacy, and which in the hands of Palmieri, 

 has already furnished valuable results. The presence in the 

 sublimations of the fumaroles of Vesuvius of the metal thal- 

 lium, which was lately obtained by Lamy from certain pyritic 

 formations of Belgium, and other countries of Europe, con- 

 firms in an unexpected manner the relations already indi- 



