METEOROLOGY. 409 



prisms. The spectrum is prolouged much further on the side of the 

 rays of great ^vave length. At tlie same meeting Egoroflf communicated 

 his researches on the absorption spectrum of the terrestrial atmos 

 phere ; he observed the electric and other lights as seen at the Paris 

 Observatory. (Mature, xxvi, p. 520.) 



Egoroff', as the result of some observations made at the Paris Observ- 

 atory on the absorption spectrum of our atmosphere, finds that dry air 

 and aqueous vapor are the only elements producing sensible effects. 

 His experiments included observations of the absorption of an electric 

 light by the layer of air between the observatory and Mount Valerian. 

 {Comptes Re7idus, Paris, November 14, 1881.) 



C. P. Smyth, in an appeal to physicists not to neglect spectroscopic 

 observations of his so-called rain-band, says: "While in Scotland a 

 rain-band of intensity marked 2 usually produces a little rain and 3 

 produces much, yet in Lisbon during the same months the so-called 

 rain-band marked 4 and yet no rainfall, but with 5 or 6, the tempera- 

 ture remaining the same, rain will come down even in that dry coun- 

 try. - - - Mr. T. G. Ejlands has accumulated much experience as 

 to the advantage of supplementing spectroscopic observations with 

 a polariscope. - - - I rather prefer the spectroscope alone, but 

 greatly increased in size and power." Professor Smyth recommends 

 as that the daily notation of the strength of the rain-band be made at 

 a fixed hour, say 9 a. m., and be recorded, not in absolute measures but 

 differentially in terms of some other band which is not connected with 

 aqueous vapor; for such comparison he recommends a low sun-band 

 which is on the yellow side of the D line. {Nature, xxyi, p. 553.) 



Ealph Abercromby says there is one case in which the rain-band may 

 give valuable information, namely, when we have a vapor-laden over- 

 current with a dry surface wind. This often occurs in winter, and with 

 a warm southwest current over an area of frost and east wind. In prac- 

 tice this almost invariably makes itself visible by the long converging 

 line of cirrus which so often precedes a rain or thaw ; but, still, cases may 

 occur where no cirrus is formed or where it is otherwise visible or where 

 it is otherwise invisible. Abercromby further says : "There are strong 

 grounds for believing that an air spectrum may vary not only with 

 the amount of pure vapor quantity, but it seems probable that its em- 

 ployment may be still further extended. There are strong grounds 

 ibr believing that an air spectrum may vary, not only with the amount 

 of j)ure vapor, but also with the size, aggregation, and physical condi- 

 tion of the condensed vapor suspended in it. For instance, take the 

 so-called rain lines. These may appear either alone or with a rain- 

 band of any intensity ; so that if the band is due to pure vapor onl^', 

 the lines must depend on some other condition. Again, in sunset tints 

 we have a natural spectroscope whose colors certainly are the product 

 of both the quantity and quality of the total moisture suspended in the 

 air. I have made a large number of observations on the lurid, coi)pery, 



