February io, 19 io] 



NA TURE 



429 



■jointly, they generally are not all in one plane of vibra- 

 tion ; in other words, one or more appear in a plane which 

 is normal to that of the others, and this can always be 

 secured by a manipulative device. The paths described by 

 any point on the string would in such circumstances be 

 ■curved figures identical with, or analogous to, the well- 

 Uno^'n figures of Lissajous. 



I send two photographs (Figs. : and 2), each only 3 cm. 

 by 2 cm., showing a short length of the string wijh a 

 brilliant point in the middle of it, when executing such 

 oscillations. The curves shown in them are only two out 

 of a large number that I have observed and photographed, 

 and can be recognised to be both compounds of the first 

 three harmonic# in the series mentioned above. It is 

 difficult at first mentally to picture the process by which 

 a tuning-fork executing normal oscillations maintains a 

 string permanently in an oscillation of the type shown in 

 the photographs. C. V. Raman. 



Post-Box 59, Rangoon. 



A Tertiary Leaf-cutting Bee. 



Although fossil remains furnish us with abundant 

 evidence of the antiquity of many structural characters in 

 animals, and permit us to surmise a like antiquity of cer- 

 tain habits, it is not often that we find preserved the proofs 

 of the latter. The leaf herewith figured, collected in the 

 Miocene shales of Florissant, Colorado, by two of my 

 students, Messrs. Duce and Rusk, shows the work of a 

 leaf-cutting bee. Evidently the specialised and peculiar 

 liabit of cutting out pieces of leaf to use in forming the 

 nest was as highly developed, perhaps, a million years 



ago as it is to-day. The bee itself has also been obtained, 

 and described as Megachile praedicta, Ckll., 1908. 



T. D. A. COCKERELL. 



University of Colorado, January. 



Tests for Colour-blindness. 

 With reference to the article on colour-blindness in 

 N.^TURE of January 27, I should like to point out that 

 advocates of the Holmgren test assume that a person who 

 ■fails with the wools will fail with coloured lights, and 

 that a person who appears normal when examined with 

 the wools is normal when examined with coloured lights. 

 This was the first point which I proposed to settle when 

 I took up the subject of colour-blindness. I found many 

 varieties of colour-blindness, unimportant from a practical 

 point of view, that failed, and many dangerous varieties of 

 colour-blindness that passed this test. Many absolutely 

 normal-sighted persons are also rejected by the Holmgren 

 test ; Germany has officially discarded it for this reason. 

 NO. 2102, VOL. 82] 



Within the last fortnight I have examined two dangerous 

 varieties of colour-blindness that passed the Holmgren test 

 with the greatest ease ; in fact, the most punctilious examiner 

 would not have suspected that there was anything wrong 

 with their colour sense, but both made the grossest errors 

 with my lantern. The first case could not tell between the 

 white, green, and red lights on trams at a distance of 

 about one hundred yards. 



The two factors which seem to be generally overlooked 

 are the great effect of diminishing the intensity of a light 

 in certain cases and the importance of taking into account 

 the size of the image on the retina, that is to say, the 

 number of cones stimulated. A few days ago I examined 

 .1 normal-sighted man who had failed with the Holmgren 

 ii-st. He put definite browns with the green skein. When 

 I found that he was normal I asked him to name the 

 wools, and he did so correctly. I then asked him why he 

 put browns with green. He replied, " I have been told 

 I am green-blind, and I thought that there. was green in 

 those browns which I could not see." When I told him 

 he was quite normal he had not the least difficulty with 

 the test. F. W. Edridge-Green. 



Hendon, January 31. 



Observations of Halley's Comet. 



Readers of Natcre may perhaps be interested to know- 

 that Halley's comet can now be seen with a good pair of 

 field-glasses. Careful estimates make it almost exactly 

 equal to an eighth-magnitude star. 



The best form of instrument is a high-power Galilean 

 binocular, and though the comet does not present any 

 interesting features with such small optical aid, it can be 

 distinctly seen, and distinguished from a star bv its 

 nebulous appearance. It is, of course, necessary to know 

 the comet's position fairly exactly before attempting to 

 pick it up. The following are a few of my notes : — • 

 1910, Jan. 8, 12 and 13, Comet faintly seen in i-inch finder 

 Mae. ± 9'o. 

 ,, ,, I5d. Sh. 45m. Faintly seen in binocular. 

 ,, .. 3od. Sh. cm. Steadily seen in binocular. 

 ,, Feb. 3d. 8h. om. Found with binocular, eighth magnitude 

 (estimate S'l). 



P. M. Ryves. 

 Zaragoza, Spain, February 5. 



Records of the Earthquake of January 22. 



Dr. Chree has noted in N.^ture of February 3 the 

 mechanical effect upon the Kew declination-magnetograph 

 by the earthquake of January 22. Any confirmation of 

 movements of this kind is of considerable value, and I 

 therefore send you this notice of the corresponding effects 

 upon the Stonyhurst magnetographs. AH the three elements 

 were markedly affected ; the declination magnet was set 

 in oscillation at 8h. 56m. a.m. for five minutes, the vertical 

 force magnet also at 8.56 for about two minutes, and the 

 horizontal force magnet was the most disturbed, com- 

 mencing at 8.52 and lasting for quite ten minutes, -n'ith 

 a maximum displacement of 3.5 mm. against the force of 

 the torsion balance, but it is not clear that there was any 

 swing on the opposite side of the normal position. 



The origin of the earthquake remains apparently un- 

 known, but, judging by our Milne seismograph, it was 

 much nearer to us than any of the thirty earthquakes 

 registered here since the instrument was fairly started on 

 active service on July i, and the proximity may account 

 for the much greater swing of the boom. From the 

 beginning I have claimed the eastern border of the Atlantic 

 for the true region. 



Prof. Milne's seismographs at Shide have shown an 

 enduring displacement which has not been produced here. 

 Walter Sidgreaves. 



Stonyhurst College Observatory, February 5. 



The Mendel Journal. 

 In Nature for December 30, 1909 (p. 252), there 

 appeared a review of the first number of the Mendel 

 Journal, by " E. H. J. S." He also, in the same review, 

 reviewed the current issue of Biometrika. I pass no com- 

 ment upon the questionable fairness of having two 



