WATER VAPOUR OX MARS. 151 



Tyndall* and Buff, have shown that, on reaching the surface 

 of the Earth, the Hght rays are changed into obscure heat, and 

 as such are radiated back into space. The}^ also found that 

 aqueous vapour, while allowing the former to pass, absorbed 

 the latter ; the same is true, in a sense, of dry air, but with this 

 difference that the power of absorption of aqueous vapour is 

 16,000 times that of dry air. The returning heat is thus absorbed 

 into the air, and serves to preserve the temperature of the under- 

 lying world. To quote Tyndall's words, 



" Aqueous vapour is a blanket more necessary to the vegetable life of 

 England than clothing is to man. Remove for a single summer night the 

 aqueous vapour from the air which overspreads this country, and every 

 plant capable of being destroyed b}^ a freezing temperature would perish. 

 The warmth of our fields and gardens would pour itself unrequited into 

 space, and the sun would rise upon an island held fast in the iron grip ot 

 frost." 



Given that in Mars, as appears from the latest investigations, 

 water vapour is present, and in larger quantities than in our own 

 atmosphere, and we have a reasonable explanation of the phe- 

 nomena observed, and it is not hard to recognise in the heat- 

 storing atmosphere thus constituted the strongest reason ^for 

 the generally temperate conditions which would appear to exist 

 on the neighbouring planet. 



GEOLOGY OF NYASALAND.— An increasing amount of 

 scientific attention has of late been given to Nyasaland. and 

 the geology of that country formed the subject of several papers 

 read at the Geological Society's meeting on November 17th. by 

 Dr. R. H. Traquair, F.R.S., and others. Nyasaland consists 

 of a series of high plateaux rising irregularly one upon another. 

 The country, is formed, for the greater part, of crystalline rocks : 

 these comprise (a) metamorphosed sedimentary beds, including 

 graphitic gneisses, with limestones and muscovite-schists : {b) 

 foliated igneous rocks, especially augen-gneiss ; (r) plutonic in- 

 trusions, usually granite or syenite, more rarely gabbro. An 

 altered sedimentary series occurs in the north-west corner of the 

 country, and of the members of this series the Mafingi Hills are 

 formed. The series consists of accumulations of quartzites, 

 grits, and sandstones of pre-Karroo age. Rocks belonging to 

 the Karroo system occur in patches in the north of Nyasaland, 

 and the system is also represented in the south. High above 

 the present level of Lake Nyasa are to be found recent lacustrine 

 marls and sands, distant as much as fifteen miles from the present 

 margin of the lake. In the northern parts pumiceous tuffs are 

 met with, and across the German East African border there is 

 a wide distribution of Tertiary and Recent lavas and tuffs. 



* Heat, a Mode of Motion, 2nd ed. 



