1870.] Physics. 5G9 



efficient performance ; other contrivances will suggest themselves 

 where stones are not procurable. Although it would seem that 

 alcohol is consumed to a disadvantage without a wick, yet practi- 

 cally the " Etna " boils water with a smaller consumption of spirit 

 than any contrivance yet tried, a good argand lamp requiring at 

 least half an ounce to do the same work as the Etna. The Eussian 

 blast lamp is still more wasteful, consuming nearly 2 ounces. The 

 superior economy of the Etna is attributed to the low temperature 

 of the wickless flame and the manner in which the boiler is wrapped 

 in the fire, no more heat being supplied than can be taken up by so 

 bad a conductor as water. The defect of all lamps giving an 

 intense flame being that heat is wasted by being supplied too 

 quickly, so that the apparently feeble fire in the gutter of the Etna 

 is more efficient than the heat of powerful lamps, as well as more 

 economical ; the latter quality is very important to the pedestrian, 

 to whom every ounce of weight is a consideration. 



P. Lewald, referring to the phenomenon first observed by Dr. 

 Fritsche, says it is not at all a correct statement that the blocks of 

 tin exposed to a cold of — 35° should alter their state of aggregation 

 from that cause ; the real cause is that the blocks of tin usually of 

 250 cubic inches capacity are cast in iron moulds, and as a conse- 

 quence thereof the tin contracts unequally, and so as to leave in the 

 inside of the blocks cavities often so large as to occupy 40 cubic 

 inches. These hollows are lined by a crystallized metal at a high 

 degree of tension. The tin at St. Petersburgh was laying heaped 

 block upon block, and the effect of the cold was simply a remote cause 

 to what took place, the weight of the blocks of metal placed on each 

 other being such as to produce necessarily a pressure too great to be 

 borne by the undermost blocks. The author says, if tin is molten 

 and allowed to cool, so as to shrink uniformly, no cold, even of — 40° 

 or less, will have the effect observed in the locality alluded to. 



L. Cailletet has studied the variation of compression of air and 

 hydrogen between 1 and 800 atmospheres. Up to 80 atmospheres' 

 pressure, air is more compressed than it should be if it followed the 

 law of Mariotte ; and at 680 atmospheres' pressure it only occupies 

 two-thirds of the space which it ought to do theoretically. The 

 method by which the author is enabled to measure the volumes 

 occupied by a gas in an opaque apparatus is very simple. The glass 

 tube is enclosed in an iron one ; the former, containing the gas, is 

 lightly gilt. The mercury which serves for the transmission of 

 pressure, whitens the gold, leaving a well-defined mark on it after 

 the pressure ceases. 



Electricity. — In a letter to M. Dumas, Professor de la Eive 

 states that he has just finished a series of experiments on the mag- 



