village. M. Berthier, the chemist, has estimated that the heat furnished daily by these springs equals that produced by the combustion of more than four and a half tons of coal, sufficient to comfortably warm the houses and even the streets.[1]
Now that the rapid exhaustion of coal-mines forces man to seek the precious combustible at increasingly greater depths, it interests us to know the extreme limit of accessible depth. The report of the English commission of inquiry contains very complete data on this point.[2] The sole cause, says the report, that can place a limit on the practicable depth of mines is the elevation of temperature. In the English mines the temperature is of marked uniformity to the depth of about 15 metres, viz., 10° Cent. From that depth the heat increases at the rate of 1° to 37 metres, so that at a kilometre of depth it attains blood-heat. This heat hinders the mining operations by heating the air that is artificially made to circulate in the mines, and rendering its effect insignificant. Regarding the question of the highest temperature man can work under without danger to health, the evidence gathered by the commission exhibits some extraordinary cases, but such of them as were verified were found to be exaggerated. Competent authorities are, however, united in maintaining that steady labor is impossible, in humid air, at a temperature approaching 37°. Heat is better supported in dry air. Now, as the deepest mines are generally the least humid, we ought, with the powerful means of ventilation available in these days, to certainly reach a depth of 1,200 metres. We may perhaps go even deeper, thanks to the system of atmospheric shafts recently introduced at Epinac by a French engineer, M. Z. Blanchet. By means of a pneumatic tube the cars are propelled and a thorough ventilation is secured at the same time. By developing this system, very deep deposits can doubtless be reached.
[To be continued.]
| CHANGES OF THE CIRCULATION DURING CEREBRAL ACTIVITY. |
By CHARLES SEDGWICK MINOT, S. B., S. D.
DR. ANGELO MOSSO, the distinguished Professor of Physiology at the University of Turin, has made some observations on the physiology of the brain which, for novelty and interest, have been equaled by but few recent scientific discoveries; for his researches lie
