SCIENCE: 



A Weekly Record of Scientific 

 Progress. 



JOHN MICHELS, Editor. 



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SATURDAY, DECEMBER 10, 1881. 



Sir — On the evening of November 24, I noticed 

 that the spectrum of the star DM. +36 3987 has a 

 bright band in the blue. The star, accordingly, be- 

 longs to the small class of objects which comprises 

 Rayet's stars in Cygnus (near this one) and Oeltzen 

 1 7681, discovered here in 1880. 



On November 25 I found a small planetary nebula, 

 undistinguish'able from a very faint star by the or- 

 dinary eye-piece, bnt detected by the character of its 

 spectrum. Its place for 1880 is in R.A. 2o h 6 m 260.4, 

 declination + 37° 3' 25". It follows W. xx 200 eight 

 seconds, three minutes of arc farther south, and is 

 followed respectively 2 s . 6 and 2^.3 by two faint stars 

 north 37" and south 20" of the nebula. 



Harvard College Observatory, 

 Cambridge, December 1, 1881. 



Edward C. Pickering. 



SHALER AND DAVIS' "GLACIERS." 1 

 By W. J. McGee. 



I. Introduction.— The extensive superficial modifica- 

 tion of the globe accomplished through the agency of 

 water in its three states of aggregation has been rendered 

 possible by certain properties peculiar to this substance, 

 chiefly (1) its powers of assuming the several forms of 

 solid, liquid, and vapor within the narrow range of ter- 

 restrial temperature, (2) its enormous capacity for heat, 

 and (3) its power of dissolving other substances. 



The temperature of the earth's surface is indeed large- 

 ly determined by the aqueous vapor contained in the at- 

 mosphere ; for if it were not for this vapor the solar 

 energy falling upon the earth would be radiated away 

 almost as quickly as received, and could exercise but 

 little influence upon temperature. The narrow range of 

 terrestrial temperature since the beginning of the organic 



1 " Illustrations of the earth's surface. Glaciers ; by Nathaniel South- 

 gate Shaler, professor of Paliontology, and William Morris Davis, in- 

 structor in Geology, in Harvard University, Boston. James K. Osgood 

 & Co., 1881." Very large 4 , pp. i — viand 1-198, pi. i— xxv and one un- 

 numbered, with twenty-five unnumbered leaves discriptive of plates. 



581 



record attests the enormous capacity and marvelous del- 

 icacy of this temperature — equalizing agent, for within 

 the limited bounds of the space separating earth and sun, 

 the temperature varies from a hundred thousand degrees 

 above to two hundred and fifty degrees below the 

 Fahrenheit zero; though accidents in this adjustment 

 are attested by the traces of successive ice periods 

 in the geological history of the globe. The influence 

 of liquid water in producing the various phases as- 

 sumed by the earth's surface, during geological time 

 has long been the subject of study ; but it is only within 

 the last forty years that the newly commensurate influ- 

 ence of ice has been detected. 



II. The existing glaciers of the earth. — The most 

 accessible of the existing glaciers are those of the Swiss 

 Alps ; and the best route for the student to pursue in 

 entering this region is to pass up the valley of the Rhone. 



Here, aside from the more obscure evidence of the 

 former great extension of the glaciers, the various works 

 of ice-action became constantly fresher in ascending the 

 river until they disappear beneath the wall of ice consti- 

 tuting the terminal portion of the glacier. At the foot 

 of this ice wall is an irregular mass of stones and earth — 

 the terminal moraitie — lying across the valley, cut in 

 twain by the muddy stream emerging from a cavern in 

 the basal portion of the glacier ; and the ice itself is gul- 

 lied by tiny rills and soiled with sand and dirt, and hard- 

 ened with pebbles and rock fragments, which from time 

 to time roll down its steep front, to the morainal heap 

 below. When the glacier shrinks for several successive 

 seasons, as occurs when the weather is unusually dry and 

 warm, the stream flowing from it becomes a torrent, 

 and the moraine may be separated from the ice front by 

 a belt of striated and polished rock, but sparsely cov- 

 ered with coarse debris ; but when the ice advances for 

 a number of years the stream dwindles, and the sheet of 

 earth and stones is pushed forward and crumpled up 

 into a mighty embankment, rising into a range of irreg- 

 ular hillocks. Many such ridges attest the various per- 

 iods of temporary advance in the history of most of the 

 secularly retreating glaciers. On ascending the ice 

 stream itself, the superficial rock-fragments, pebbles, and 

 earth are found to he mainly in parallel bands, or medial 

 moraines; and on tracing these to their origin, each is 

 seen to consist of the two lines of matter constantly 

 tumbling down the valley sides or lateral moraines 

 which are brought into contact whenever two glaciers 

 meet and merge into one. Thus the number of branches 

 uniting to form any glacier can be determined from the 

 number of parallel bands on its surface. The ice-stream 

 occupies a crooked and irregular valley, the rate of its 

 motion varying with the declivity, regularity, and width 

 of the channel, just as does that of liquid rivers ; though 

 wherever there are considerable irregularities in the 

 channel the strain produces cracks and fissures 

 which gradually widen and form crevasses, or even, 

 where there is a sudden increase in declivity, separates 

 the ice into a mass of irregular pyramidal blocks, or 

 ser acs; but when a more uniform stietch of gentle slope 

 is reached the seracs re-unite, and the crevasses close, 

 transforming the fragmentary mass again into a solid, 



