556 



NA JURE 



\_April 14, 18S1 



magnitude, and the other a blue 9. The contrast of colours 

 was very striking, but there was little difference in size. In a 

 letter recently received from the Rev. Mr. Webb, I find that it 

 was previously observed by him, and it appears as one of his 

 own discoveries in the second edition of " Celestial Objects," 

 published in 186S. The red star is there classed as 6'5 ma_'., 

 and the blue as S. The two stars, therefore, appeared to difier 

 very considerably in magnitude wlien seen by Mr. Webb, while 

 to me, eleven years subsequently, they seemed quite nearly equal. 

 Hence I conclude that the red is a variable, and I wish to cill 

 the attention of observers to it while it still remains in view, liy 

 a rough measurement I make out its position for i88l = a 

 7h. lom. 44s,, and S - 23° 6''6. John Birmingham. 



Millbrook, Tuam, April g 



Concealed Bridging Convolutions in a Human Brain 



In his work on the " Convolutions of the Human Brain " 

 Ecker denies explicitly that the first and second external bridging 

 convolutions of Gratiolet, as seen in Cercopithecus, Inuus, &c., 

 are ever concealed, either in the higher apes or in fcetal or adult 

 man. I have however in my possession an adult human brain 

 in which (7 convolution nearly corre-p ending in position to the 

 external bridging one of Gratiolet is concealed, while another 

 slightly external to it is nearly so. The brain was hardened in 

 nitric acid with the membranes on (a much preferable method, 

 by the by, to that of first removing the membranes ; as these, 

 by absorbing the acid and swelling, serve, like so many wedije^, 

 to keep the convolutions apart, and prevent the shrinkage that 

 otherwise takes place). There was no indication of any con- 

 cealed convolution until the membranes, just moistened for the 

 purpose with water, were being removed. Then, owing to the 

 opening out of the sulcus occipitalis transversus of Ecker, the 

 tip of one became visible, and this tip, even now that the edge< 

 ot the sulcus are widely separated, is from one-eighth to one- 

 sixth of an inch beneath the general surface. 



Its position relative to the great longitudinal fissure and to the 

 posterior border of the gyrus supramarginalis seems to me pretty 

 accurately to correspond to tliat of the external bridging convo- 

 lution to those parts in the brain of an Indian pig-tailed baboon 

 of undetermined species with which I have compared it ; but in 

 the latter the sulcus occipitalis transversus does not exist, while 

 in this human brain, as is very common, the lateral or horizontal 

 portion of the fissura parieto occipitalis, beneath the bevelled 

 edge of which in the baboon the convolution lies concealed, has 

 a very short coui'se indeed. 



The only difference then is that in the one specimen (the 

 human) the concealed convolution lies in the transverse occipital 

 fissure, there being no lateral extension of the parieto-occipital 

 fissure, w-hile in the other it lies in the parieto-occipital fissure, 

 the transverse fissure not existing William Carter 



Liverpool, March 26 



Sound of the Aurora 



If I had consulted Franklin's account of his Polar researches 

 before I sent you my extract from Tacitus, I should nut have 

 revived the question of sounds being heard with the aurora 

 borealis. Franklin and his companions watched the aurora 34^ 

 times in two successive winter seasons ; and never once, he says, 

 did they observe a sound. Were, then, the experiences quoted 

 by your other correspondent and myself mere illusions? Per- 

 haps not. Franklin made his observations at and about the 

 southern shore of Bear Lake, in latitudes varying from 67° to 

 69'' north ; might not the greater volume of air through which 

 the phenomenon had to pass in reaching our island have causeil 

 the electric fluid to work up a sound ? Surely that is possible 

 The attractive force of the aurora is — we learn from Franklin 

 himself — increased within a certain limit as its rays proceed 

 southwards ; for whereas Parry and his party at Port Bowen in 

 latitude 73° 15' noticed no deflection of the compass-needle under 

 the influence of coruscations, Franklin and his party on the 

 shores of the Beai' Lake, six degrees further south, constantly 

 observed thii efteot. And the attractive force is strongly felt 

 here — hindering telegraphic communication at all events. Might 

 not the vibratory force not sensible at within so short a distance 

 from its origin as the attraction be increased within a greater 

 limit? M. L. Rouse 



Sunnymead, Chislehurst Common 



PERIODIC OSCILLATIONS OF BAROMETRIC 

 PRESSURE 



'HPHE MSS. of the accompanying article, which was 

 -'■ left unfinished by the late :\Ir. John Allan Broun, 

 F.R.S., were handed over to me some time ago by Prof. 

 Balfour Stewart, with a request that I would put them 

 into shape for publication. 



I have not found it necessary to make many alterations 

 in, or additions to the original, and where made they are 

 mostly indicated in initialed foot-notes. 



E. Douglas Archibald 



In an article which appeared in Nature (vol. xix. p. 6) 

 a remarkable relation was shown to exist between the 

 annual ranges of the atmospheric pressure and of the 

 temperature of the air, as derived from the monthly 

 means obtained from several years' observations of the 

 barometer and thermometer at certain stations in India. 

 The results and the conclusions from them do not appear 

 to have been always understood, and as they bear on 

 some of the most interesting questions on meteorology, 

 I shall now examine them anew with the aid of obser- 

 vations at some other stations, under different local 

 conditions. 



For this end it is desirable to employ some elementary 

 considerations. Let us, first of all, consider the action 

 of varying temperature on a vertical column of , 



the atmosphere. Let us consider a column of I 

 air reaching from the soil at B to the upper limit I 

 of the atmosphere at A ; and suppose that the 

 pressure shown by a barometer at E is 30 inches, | 

 while at a higher station, C, it is only 20 inches. 

 If, now, the column of air is heated so that the 

 temperature of the part F. C is increased by 10^ F. 

 we know from laboratory experiments that the 

 air will expand, so that a part of that which was 

 below c will be pushed above it, and while the 

 barometer at p, will continue to show 30 inches, 

 that at C will show 20'2 inches, the mercury at C 

 will have risen tw'O-tenths of an inch. 



If, now, we suppose that the mass of air re- 

 mains constant throughout the year, there will 

 be an annual variation of the barometer at C, 

 where its height will be greatest in the warmest 

 month and lowest in the coldest month. For 

 the same reason the ditterence of the barometric 

 heights at n and C will be least in the warmest month 

 and greatest in the coldest. 



It has been supposed that the mass of the atmosphere 

 remains constant throughout the year ; if this is not the 

 case the variations of pressure at C will not depend on 

 temperature alone, but also on the other causes which 

 produce variations at D. 



In Nature, vol. xx. p. 55, Mr. Douglas Archibald has 

 given a series of dift'erences of barometric heights at high 

 and low stations in India for the months from (Jctober to 

 .April. The month of lowest mean temperature, January, 

 shows always, as in the case just supposed, the greatest 

 difference of pressures. As the high and low station is 

 never in the same vertical, the one being sometimes 300 

 miles horizontally distant from the other, it is difficult to 

 eliminate the part of the variation due to temperature at 

 the higher station, but if we take as an approximation, 

 however rude, the mean of the temperatures at the two 

 stations as that of the vertical column, we can see that a 

 considerable part of the variation at the upper station 

 may be due to the expansion of the column with tem- 

 perature. 



Thus for Leh and Lahore the mean temperatures and 

 difference of barometric heights are ' : — 



' The numbers are taken from the work cited by Mr. Archibald, " The 

 Indian Meteorologist's I'ade jVecum," by Mr. H. F. Blanford, Pt. ii. pp. 



