OcTOBEB 12, 188:?.] 



SCIENCE. 



491 



time a similar moist region, of 15° altitude and 

 perhaps 35° length, was discovered in the south- 

 east ; and this in turn was found fifteen min- 

 utes later to he partly filled with cloud. After 

 an hour or so they had all disappeared. Tlie 

 appearance was as though a body of air heavily 

 charged with moisture, having liecome heated, 

 w!is seen rising bodily at six o'clock, while at 

 seven the conso(]uent cooling had condensed 

 in part its moisture. 



One of the most striking facts noted is the 

 suddenness with which a hygrometric change 

 occurs, as indicated by the spectroscope. 

 During the fine weather of June 30 and Jul}' 

 1, the spectroscope had indicated unusually 

 dry air with almost absolute uniformity. Dur- 

 ing July 1, as the diagram shows, there had 

 been a very slight increase in the moisture 

 present, as indicated by an observation at six 

 P.M. Fifteen minutes l.-iter, happening to 

 glance through the spectroscope, I was greatly 

 surprised to see how much blacker the line 

 looked. A new set of readings was taken, 

 giving a much higher amount of moisture, as 

 inilicateil by the sudden rise in the curve. 

 The sky was almost entirch" free from clouds, 

 with a light breeze from the south - west. 

 Measurements were made in both cases all 

 along the western half of the horizon, the 

 eastern being too dark at that hour. At seven 

 o'clock a moderately dense bank of stratus 

 clouds had risen in the west to an altitude of 

 1.5° or 20°. The record at seven and seven- 

 thirty showed little further hygrometric change. 

 The skj' was soon entirely overcast with clouds. 

 This hygrometric change was not a mere mo- 

 mentary one, connected with cloud-formation ; 

 but the later record showed it to be the begin- 

 ning of a period of moist air and showery 

 weather. The hygrometer, it will be noted in 

 the diagram, gave little sign of change for 

 some hours. Other sudden changes of equally 

 striking character have been observed. Tliat, 

 as has been suggested by Capron and others, 

 the physical state of the suspended water, the 

 size of the a(iueous particles, maj- have an influ- 

 ence in its light-absorbing power, and so ex- 

 plain in part such changes, is verj' possible ; 

 but the evidence that such is the case appears 

 to be far from conclusive. 



It is believed that a series of spectroscopic 

 oliservations, continued for a considerable 

 period of time at different stations, would 

 give much light on a number of important 

 questions in meteorology, particularl3' in the 

 study of the formation of showers and storms. 

 The instrument is apparently admirably adapt- 

 ed to do this work, by its abilit3' to trace 



accurately the motions of masses of vapor in 

 the upper atmosphere. The discussion of the 

 more important (luestions wdiich arise in carry- 



.July l.p.M. 



.luly 2, A.M. 



iiig on this investigation is deferred until a 

 larger mass of figures and facts have been 

 accumulated. C. S. Cook. 



NOTES ON SASSAFRAS-LEAVES. 



There are three distinct forms of sassafras- 

 leaves. The simplest is ovate, varying to 

 oval and obovatc. A second form is three- 

 lobed, the incisions running from near the 

 middle of the upper half of the leaf's edge to 

 the centre of the blade. The third form- is 

 midway between the entire and three-lobed 

 sorts, and has but one side-lobe ; the opposite 

 half of the leaf being entire. It is as if one- 

 half of a three-lobed leaf were joined by the 

 midrib to the opposite half of an entire one 

 of the same size. This form may be very ap- 

 propriately called the ' mitten.' 



In the study of these three forms, branches 

 of sassafras have been gathered from a large 

 number of places through the • surrounding 

 country. Some have been obtained from the 

 woods, and others from the open field. 

 Branches were cut from the largest trees and 

 fiom the smallest, from vigorous trees and 

 those of slow growth. Ten hundred and fifty 

 leaves were examined : and of these, five hun- 

 dred and thirteen were entire; four hundred 



