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Phosphorus, as has been shown by M.Van Marum, burns in an atmosphere rare-fied 60 times; and I found that phosphu-retted hydrogene produced a flash of lightwhen admitted into the best vacuum thatcould be made, by an excellent pump ofNairn’s construction.

The mixture of chlorine and hydrogeneinflames at a much lower temperature thanthat of hydrogene and oxygene, and pro-duces a considerable degree of heat in com-bustion; it w.as therefore probable that itwould bear a greater degree of rarefaction,without having its power of exploding de-stroyed ; and this I found by many trials isactually the case, contrary to the assertionof M. de GROTTHUS. Oxygene and hy-drogene in the proportion to form water,will not explode by the electrical sparkwhen rarefied eighteen times, but hydrogeneand chlorine in the proportion to form mu-

somewhat lower than in arithmetical progression, thepressure decreasing in geometrical progression.

There is, however, every reason to believe, that thetaper would be extinguished at a height of between 9and 10 miles, hydrogene between 12 and 13, and sulphurbetween 15 and 16.