124 



SCIENCE. 



[Vol. VII., No. 157 



tributious for this purpose are asked of Italian pale- 

 ethnologists, and of sach foreign friends as may 

 choose to forward their offerings to Professor Pelli- 

 grino Strobel, at Parma. Henry W. Haynes. 

 Boston, Feb. 1. 



The moon's atmosphere. 



I would be glad if James Freeman Clarke would 

 explain the projection of a planet on the moon's face 

 by the refraction of an atmosphere, as implied in his 

 letter to Science of Jan. 8. Would not the rays from 

 the planet pass through the atmosphere in a curve, 

 and reach the eye of the observer in a tangent to 

 that curve at the point where it leaves the atmos- 

 phere ? If so, then, as this tangent would lie without 

 the moon's disk, the planet could not, by refraction, 

 appear projected upon it. W. G. Blish. 



Niles, Mich., Jan. 21. 



After reading the question by Mr. Blish in regard 

 to the phenomenon described by me, viz., of the pro- 

 jection of the disk of Jupiter on the face of the moon 

 at the moment of occupation, I addressed notes to 

 Prof. Edward C. Pickering of Harvard observatory, 

 and Prof. B. A. Gould, asking for their opinions in 

 the matter. Both have kindly answered me. and I 

 transmit a portion of their letters for publication. 

 It will be seen that they agree in the main with Mr. 

 Blish, that refraction by a lunar atmosphere can 

 hardly explain the phenomenon. 



James Freeman Clarke. 



Jamaica Plain, Mass., Feb. 1. 



[From Professor Pickering.] 



" A homogeneous and quiet lunar atmosphere 

 would pretty certainly not account for the apparent 

 projection of a star or planet on the disk of the 

 moon, although a disturbance in the atmosphere, 

 either of the moon or of the earth, might momenta- 

 rily confuse the images viewed through it. I should 

 prefer explaining the phenomenon by the physiologi- 

 cal effect of irradiation, which increases the apparent 

 size of bright objects, and so might make two disks 

 seem to overlap each other when they were merely 

 tangent." 



[From Professor Gould. J 



"The phenomenon which you observed, is, I am 

 inclined to believe, by no means an uncommon one, 

 although, as is natural, the published accounts of it 

 relate chiefly to bright fixed stars, rather than to 

 planets. 



"I fear that refraction by a hypothetical atmos- 

 phere would not explain the phenomenon adequately, 

 although it seems to me that Mr. Blish has overstated 

 his case, and that the ray emerging from the atmos- 

 phere would not necessarily be tangent to the curve 

 at the point of emergence. Turning to Herschel's 

 'Outlines of astronomy,' — a convenient though not 

 altogether trustworthy book, — I find the same phe- 

 nomenon mentioned in a footnote to art. 414. He 

 speaks of it as an ' optical illusion,' which perhaps it 

 is ; but calling it by that name does not explain it. 

 I myself have seen it, and believe that it has 

 been noted by most observers of occupations, and I 

 have seen attempts to explain it by 1 irradiation ' and 

 by indentations in the moon's limb ; but I have never 

 seen any explanation which has appeared to me 

 satisfactory. It belongs to the same class of phe- 

 nomena as the ' black ligament,' seen when an in- 

 ferior planet transits the solar disk. This has never, 



to my knowledge, been satisfactorily explained 

 either." 



Festoon clouds of a tornado. 



The clouds so termed by your recent correspondent 

 were more strikingly exhibited than I remember ever 

 to have seen them, on the 17th of June, 1882. They 

 formed the under surface of the high advanced sheet 

 overhanging the memorable tornado that destroyed 

 Iowa college and one-third of the town of Grinnell. 

 Other terms referred to by your correspondent more 

 properly describe the appearance, such as sand-bags, 

 droplets, mammillary cloud, or they might be spoken 

 of as innumerable filled pockets hanging from the 

 under surface of the sheet. It was first seen by me 

 in the western sky at 7 p.m., after a bright sultry 

 day. Near 8 p.m. the whole west was filled with 

 heavy clouds transfused with gold. A fierce thunder- 

 storm followed, and passed by. Immediately after 

 this there was a dead calm for a brief time, and 

 then, at 8.45 p.m., the sudden destructive funnel- 

 cloud. It was a local storm, traced a hundred miles, 

 more or less. 



Since then I have watched every threatening sky, 

 and have noticed the same phenomenon, less strik- 

 ingly shown, in at least a dozen instances, alike in 

 local or limited thunder gusts, widely extended 

 storms, and in rainless skies overspread by wild- 

 looking clouds. A splendid exhibition of the last 

 mentioned was seen at sunset last summer. The 

 whole sky was overcast by gilded cloud showing the 

 1 sand-bag ' feature, but in larger bags, either abso- 

 lutely so, or because drifting at a medium cloud- 

 height and overhead. No evidence of rain, nor any 

 unusual surface winds, preceded, attended, or followed 

 on this occasion. H. W. P. 



Grinnell, Io. 



Death-rates among college graduates. 



The recent death of Charles W. Sanborn of New 

 Hampshire is the occasion for calling attention to a 

 remarkable fact. 



His death is the first that has occurred in the Dart- 

 mouth college class of 1872. Sixty-nine men gradu- 

 ated, and for thirteen and one half years their num- 

 ber has continued unbroken by death. The Chandler 

 scientific class of the same year early lost one man 

 from eleven who graduated. 



The deaths in the two preceding and nine succeed- 

 ing classes to 1872 are recorded as follows : — 



Class. 



No. graduated. 



Deaths since graduation. 



1870 



50 



11 



1871 



68 



9 



1873 



71 



4 



1874 



63 



5 



1H75 



4S 



1 



1878 



69 



4 



1877 



54 



2 



1878 



74 



3 



1H7A 



46 



8 



1880 



48* 



1 



1881 



49 



3 



* One died just before commencement, and received 

 degree post obit., but is not included here. 



Edwin J. Bartlett. 



Jan. 28. 



