930 Transactions of the American Institute. 



different from any known substance, and was miraculously furnished 

 to them. 



Dr. J. "W. Richards said that the Jewish manna seemed to have 

 been an animal product, resembling what is called honey-dew, the 

 exuviae of small animals found under certain trees, mostly beech trees, 

 at certain seasons ; but that there is now nothing known anywhere 

 corresponding to the description of manna. 



Dr. J. V. C. Smith expressed the belief that the very pot of manna 

 put up to be kept for generations, would yet be discovered. 



Suspended Railway. 



A model of a street railway, suspended from the houses, and not 

 interfering with the street below, and especially adapted to narrow 

 streets closely built up with brick buildings, was exhibited by Julius 

 H. Striedinger. 



On the Determination of the Invisible Aqueous Vapor in the 

 Inaccessible Upper Strata of the Atmosphere. 

 Prof. Yan der Weyde — Early in this century Leslie measured the 

 clearness of the sky by the radiation from the bulb of a differential 

 thermometer placed in the focus of a horizontal parabolic reflector. 

 The mirror being a polished surface radiated no heat, but merely 

 reflected that radiated by the bulb. If the sky was clear, the heat 

 would be radiated, and there would be no return, and the thermometer 

 would fall; but if there were clouds, the thermometer would remain 

 stationary. Leslie states that sometimes when the sky is clear, the 

 thermometer will fall fifty degrees ; and at other times, when it is 

 apparently just as clear, it would not fall at all ; and at that time this 

 anomaly was unexplained. Experiments have recently been made by 

 Tyndall on the radiation of heat through different vapors. All gases 

 and vapors absorb heat; but common air, nitrogen, hydrogen and 

 oxygen, absorb the least. He found, for instance, that the vapor of 

 patchouli absorbs fifty times as much heat as common air ; and that 

 other vapors absorb still more. And he found that the vapor of water 

 is the great cause of absorption of heat by the air. A moist atmos- 

 phere acts like a valve, admitting to the earth the intense solar rays 

 of heat, and preventing their radiation. It is found, therefore, that 

 the amount of cooling of the differential thermometer indicates the 

 amount of invisible moisture in the atmosphere. When clouds are 

 formed, radiation is entirely stopped. 



