June 22, 1905J 



NA TURE 



175 



thariscope into a dark room he will notice that the first 

 visible effect is a slight general luminosity when the visual 

 gaze is directed down the optical centre of the little tube. 

 If, however, the gaze is shifted to the side of the tube, the 

 whole spinthariscopic display with its scintillating flashes 

 becomes distinctly visible. On opening the door of the 

 dark room and going into the daylight the subsidence of 

 the central and peripheral responses can be followed, whilst 

 on returning to the dark room the re-appearance, first 

 peripheral and then central, can be observed with great 

 distinctness. The essential difference between the light- 

 adapted eye and the dark-adapted eye is thus readily 

 demonstrable, and the rapidity, as well as the efficiency, of 

 such adaptations can be easily followed if the eye is sub- 

 jected to appropriate periods of darkness and of light. 



It is evident that with such a minimal test the influence 

 of a large number of other conditions may be investigated. 

 Without going into these, I may mention one of consider- 

 able interest. If the observing eye is kept in the dark- 

 adapted stage by means of a removable bandage, whilst 

 the other eye is subjected to periods of darkness followed 

 hy daylight illumination, then the visible effects in the 

 dark room still indicate modification. In my own case 

 illumination of one eye causes a distinct lowering of the 

 retinal excitability of the other one, this being especially 

 characteristic of the peripheral region of the retina. In 

 this connection it should be remembered that the pigment 

 cells alter in the frog as the result of illumination, and 

 that this alteration has been shown by Engelmann and 

 v. Gendre to occur when, the eyes being kept dark, the 

 skin of the frog is illuminated ; one eye thus influences 

 the other. The spinthariscope with its constant minimal 

 excitation affords a means of demonstrating this con- 

 sensual effect. It appears to me that with slight modifi- 

 cations the instrument may become of considerable clinical- 

 value. For clinical use it has the merit of being portable 

 and easily used. It furnishes, with no apparent decrease 

 through time, use, &c., a constant and continually re- 

 curring stimulus which is of threshold exciting value. It 

 can be easily applied to either the central or peripheral 

 portions of the visual field, and gives indications which 

 are comparable with each other, and are only altered 

 through alterations in retinal excitability. No doubt it can 

 be modified in form so as to be still more useful from the 

 clinical point of view, but even in the form in which, as 

 a scientific toy, it is now presented, its use will show 

 whether the central or peripheral retinal excitability is 

 abnormal, and I anticipate that before any changes can 

 be observed with the ophthalmoscope, it will be possible 

 by its means to ascertain alterations in retinal excitability 

 in the early stages of disease. Francis Gotch. 



Physiological Laboratory, Oxford, June lo. 



Solar Changes and Weather. 



In N.4TURE of June 8 (p. 129) Dr. Lockyer says : — " [//> 

 to the present time " (italics mine) " those who have been 

 attempting to explain variations of weather on the sup- 

 position of solar changes have been looking for the effect 

 of solar action as either increasing or decreasing simul- 

 taneously the rainfall over the whole earth." 



This is, I think, somewhat inaccurate. The possibility 

 of a given phase of solar change being causally related to 

 opposite weather conditions in different regions has been 

 recognised by many, if I mistake not, for a considerable 

 time. I might instance M. Angot, who expressly affirms 

 it in his "Traits de M^teorologie," published a few years 

 ago ; and what he there says on the subject indicates a 

 certain currency of the idea previously, of which (no 

 doubt increasing) currency back volumes of N.ituee and 

 other serials give evidence. The idea of a barometric 

 see-saw in Asiatic regions, connected with sun-spots, was 

 discussed in N.wure so far back as the 'seventies, if I 

 remember rightly. A. B. M. 



With regard to Mr. A. B. M.'s remarks above, may 

 I, in the first place, mention that I am familiar with 

 some of the meteorological researches of such high authori- 

 ties as Chambers, Meldrum. Blandford, Eliot, Hann, 



Angot, &c., but still there seems to be a tendency for the 

 solar changes, that is, changes indicated by sun-spots, to 

 be considered as affecting the whole earth simultaneously 

 at any one epoch. It would have been more correct for 

 me to have written " Up to the present time many of those 

 who have, &c.," than " Up to the present time those who 

 have, &c.," but at the time of writing I was considering 

 more the generally conceived impression as to the relation 

 between sun-spots and meteorological changes than the 

 results of investigation of any particular region on the 

 earth's surface. 



To take a case in point, two years ago M. Charles 

 Xordmann (Comptes reiidiis, vol. cxxxvi., p. 1047, May 4, 

 1903) communicated to the Paris Academy of Sciences a 

 paper entitled "La Period . des Taches solaires et les 

 Variations des Tempi5ratures moyennes annuelles de la 

 Terre." This title implied that the solar changes were 

 affecting the whole earth similarly, but the investigation 

 was only restricted to the equatorial regions, where the 

 conditions are most favourable for such an inquiry. 

 Further, I am inclined to think that the result he obtained 

 will be found to apply only to that portion of this equatorial 

 belt lying between about longitude 40° E. and 140° E. 

 The reason for this is that out of the thirteen stations in 

 all which he employed, eight were included in this_ region 

 (five stations of which were given double the weight of 

 the others), and only five were situated in the other part 

 of the belt. If it were possible to include more stations 

 in the western hemisphere, the relation between tempera- 

 ture and sun-spots which he obtained might probably be 

 reversed. William J. S. Lockyer. 



Solar Physics Observatory, South Kensington. 



Fictitious Problems in Mathematics. 



On reference to § 156 of " Rigid Dynamics," it will be 

 seen that the definition there given is identical with that 

 contained in Dr. Routh's letter of May 25, with the ex- 

 ception that the words "When the bodies . . ."occur in 

 my edition instead of " W'hen bodies . . . ." No state- 

 ment is made as to what is meant by saying that a body 

 is perfectly rough, and it is against this latter mode of 

 expression that my attack is directed. For this reason it 

 mav be maintained that the definition given in the book 

 in which the problem occurs is inapplicable to the problem 

 as at present worded. Otherwise we appear to be dealing 

 with a plank such that in the given circumstances, one of 

 which is resting on a smooth table, the amount of friction 

 necessarv to prevent sliding can certainly be called into 

 play, and this is apparently inconsistent with Dr. Routh's 

 interpretation. 



I would challenge your correspondent, " An Average 

 College Don," to point to any text-book containing an 

 explicit definition of a perfectly rough body (not bodies) ; 

 also a perfectly smooth body. If he succeeds, I anticipate 

 no difficulty iii furnishing him with examples of questions 

 which are either inconsistent with his definition, are 

 ambiguously worded, or are open to some equally serious 

 objection. ' G. H. Bryan. 



History of a White Rhinoceros Skull. 



The interesting specimen of the skull of the white 

 rhinoceros {R. simus) referred to by Prof. H. F. Osborn, 

 of the American Museum of Natural History, New York, 

 in -Nature of June S (p. 127), was, thanks to the kind- 

 ness of Mr. Graham, carefully examined by me before its 

 sale. Its chief interest lay in the fact that the horns 

 had never been detached, and consequently showed the 

 true position of the nasal horn in this species ; it was at 

 right angles to the downward sloping surface of the nasal 

 bones, thus bringing it into a most efficient position for 

 attack. 



There is a fine skull of this species in which the horns 

 have been placed in their true position ; it is numbered 

 2154 in the osteological series of the Museum of the Royal 

 College of Surgeons. The animal was shot by Gordon 

 Cumming. 



The length of the nasal horn is 860 mm. (34 inches). 

 , C. Stewart. 



NO. i860, VOL. 72] 



