Atis;. 2 2, 1872] 



NATURE 



329 



There is a clear passage into the polar area, and probably up to 

 and beyond the pole ; and wi hin this area there is a continual 

 diminurion of bulk cf the entering water as it becomes cooled, 

 as well as a continual subsidence of 'he surface water, producini( 

 a partial depression to be constantly filled by water from the 

 south. Experiment proves that if at one end of a vessel of warm 

 water ice is applied at the surface, the cooled water instantly 

 sinks, and its p ace is taken, not by water rising upwards from 

 below, but by a horizontal movement of the surface gradually 

 propagated to the other end of the vessel, while the descendinij 

 cold water creeps along the bottom, and gradually acquiring a 

 higher temperature, rises and completes the circuit. It is some- 

 what ditTicuIt to conceive, theoretically, how such a circulation 

 can commence, because the cooled atoms of water must displace 

 others before they can descend, and these again must displace 

 others, and so on over the whole mass. The amoimt of energy 

 due to the uperior weight of the first-cooled atoms mav appear 

 inaderpnte to peribrm so much work, but nevertheless circulation 

 does commence and indefinitely continues so long as a difference 

 of tempera'ure of the two ends of the vessel is kept up. The 

 extreme mobility of the particles of water, and the almost total 

 absence ot friction between them, seems t») be influential in pro- 

 ducing this resul' ; and if. is not probable that any minute differ- 

 ence of level that may be caused on the surface of the water by 

 clitference of temperature has anything to do with the motion ; 

 and I cannot help thinking that the supposed six-feet incline 

 fro'n the eiptator to lat. 60" is, if it exists, by no means an 

 elTective cause of the oceanic circulation. 



Alfred R. Walla.ce 



T TiiivK the root of Mr. Croll's difficulty (see Naturf,, 

 p. 324) is to be found in his overlooking the possibility of energy 

 becoming potential in the distribution of oceanic water. 



Water running in any direction in the norih**rn hemisphere 

 tends to swerve to its own right, and if this tendency is checked 

 (as it is in fact by the presence of continents) its layers of equal 

 density will he tilted up on the right, the limit of tilt being the 

 ang e whose tangent is the quotient of the tendency to swerve by 

 the force of gravity. This consideration is, I think, sufficient to 

 deprive .Mr. Croll's arg\iment of one of the two legs on which it 

 stood. 



Mr. Ferrel's argument from the tides is quite conclusive in 

 showing that the forces arising from difference of temperature are 

 of sufficient magnitude to keep up an oceanic circulation. Thus 

 the other leg of .Vlr. Croll's argument is gone. 



Mr. Croll may well retract his previous assertion that the 

 dirterence of k-nvtic energy is consumed in friction, for he was in 

 a fair wav to firing the earth to a standstill. 



r.righton, August 20 J. D. Everett 



Spectrum of Aurora 



A FIN", aurora was seen at Bedford on Thursday night between 

 midnight and one o'clock. It was brightest under the Polar 

 Star near the horizon, where the colour was a pale green ; whilst 

 overhead the hue often changed to a rosy red. On directing a 

 spectroscope at the most brilliant part, a bright green line 

 (W. L. 557) was very distinct, and two or three faint nebulous 

 jiands more refrangible were visible ; but the red line was not to 

 be seen, though carefully looked for on the rosy parts of the 

 aurora. Objects around were faintly illuminated as if by a 

 young moon. At one time two very faint pale green streamers 

 were seen stretching from the north to a little east of the zenith. 



Blackheath, August II J. P. Macle\r 



The Method of Least Squares 



As the wording of Prof. Hall's letter in Nature for July 25 

 might imply that he was calling attention to evidence that would 

 cliange the opinion expressed in my letter, it seems to me worth 

 while to state that at the time of writing that letter I was 

 acquiinted with the passages in question, and to repeat my 

 asserticm that with re'erence to the iih-llwd of least sijiiairs I 

 should not regard the neglect of Lagrange's memoir as an 

 omission. Also in spite of Encke's and Prof. Hall's remarks, I 

 think it has received as much attention as, viewed practically, its 

 iaip'.vtancc entitled it to. 



With regard to the principle "of 'the Arithmetic Mean, I may 

 add that I have devoted the greater part of a tolerably long 

 memoir to its consideration, and feel sure that no remarks on the 

 subject contained in a few lines could be rendered even intelli- 

 gible. J. W. L. Glaisher 



Blackheath, August 1 1 



NOTES 



We are informed that M. Faye will in all probability be M. 

 Delaunay's successor as Director of the Observatory at Paris. 

 In the meantime M. Matthieu supplies his place /ra tciii. 



The French Academy has elected two foreign correspondents 

 in the section of botany — M. Planchon in the place of M. Lecoq, 

 and M. Weddel in the place of Prof. Mohl. 



The American Association for the Advancement of .Science 

 ivas to commence its sittings yesterday at Dubuque, Iowa. Prof. 

 J. Lawrence Smith, of Louisville, had been elected President, 

 and Prof. Alexander Winchell, of Ann Arbor, Vice-President. 

 It was annoimce<l that the citizens of Dubuque had determined 

 that all members attending the meeting should be entertained at 

 their private residences free of charge during the session ; and 

 their travelling expenses would also probably be remitted by the 

 various railroad and steam':ioat lines. A very successful meeting 

 was anticipated. 



At the recent combined First C.A., First B.Sc, and Pre- 

 liminary Scientific (M. I?.) Examinations of the University of 

 London, Mr. J. M. L'ghtwoo 1, of Trinity Hall, Cambridge, 

 obtained the Exhibition in Vlathema'ics and Philo ophy ; Mr. 

 R. E. Carrington, of Guy's Hospital, the Exhibitions in Chemis- 

 tiy and in Zoology ; and Mr. J. C. -Saunders, of Downing Col- 

 lege, Cambridge, the Exhibition in Botany. 



We regret to announce the death of Mr. Freilerick Carpenter 

 Skey, C. R., F.R.S., which took place on Thursday last at his 

 residence, Mount Street, Grosvenor Square. Mr. Skey was in 

 his 73rd year. He was in early life a pupil of the celebrated 

 Dr. Abernethy, to whom he was articled in l8r6 by the Royal 

 College of Surgeons. About 1826 he was appointed De non- 

 strator of Anatomy at St. Bartholomew's Hospital. Sub- 

 sequently he founded the AlJersgate School of Medicine, which 

 became one of the largest in London. From that time to his 

 death Mr. Skey enjoyed the reputation of being in the first rank 

 of London surgeons. His writings on molical subjects were 

 numerous and impottant, and on subjects connected with sani- 

 tary science his communications to the public journals were 

 frequent. 



The f jllowing is the list of candidates who have been success- 

 ful in obtaining Royal exhibitions of 50/. per annum each for 

 three years in the Science and Art Department, and free admis- 

 sion to the course of instruction at the following institutions: — 

 To the Royal School of Mines, Jermyn Street — William Carter, 

 Ambrose R. Willis, and Alexander Gibson. To the Royal Col- 

 lege of .Science, Dublin — Arthur G. Meeze, Denis Coyle, and 

 Ernest H. Cook. 



A NATURAL History Society has been formed at Madrid called 

 " La Sociedad Espanola de Vlistoria Natural," under the presi- 

 dency of Don Jliguel Colmeiro. The first part of its publication 

 has reached this country, and contains the regulations of the 

 Society, an account of the meetings held by it up to this time, 

 and papers by Poey on Ichthyology, by Colmeiro on the Fumi- 

 tories of Spain and Portugal, by E^pada on the Volcano of 

 Ansango, by Solano on a .Meteoric Stone, by E~pada on New 

 America Ba'nchians, and by Perez Areas on New Reptiles and 

 Insects of the Spanish Fauna. It is extremely well printed, and 

 is illustrated by three capital plates. The subscription to the 



