Sept, 9, 1875] 



NATURE 



405 



adduced to prove that the corona is a real object, a matter 

 radiating by itself. The existence of a solar atmosphere slla- 

 ated beyond the chromosphere— an atmosphere which M. 

 Janssen had recognised in 1871, and proposed to call the coro- 

 nal atmosphere— thus receives confirmation. 2. Height of the 

 coronal atmosphere. In 1871 Dr. Janssen announced that the 

 coronal atmosphere extended from half the sun's radius to a 

 whole radius at certain points. This assertion has been con- 

 firmed not only by the direct views of the phenomenon, but also 

 by photography. At Dr. Janssen's request Dr. Schuster took 

 photographs of the corona with exposures of one, two, four, and 

 eight seconds. In this series of photographs the height of the 

 corona increases with the time of exposure. The height of the 

 corona in the eight-seconds' photograph exceeds at some points a 

 solar radius. (It is true that we ought to take account of the 

 influence of the terrestrial atmosphere. ) 3. As the sky was not 

 of perfect clearness at Bangchallo, Dr. Janssen observed phe- 

 nomena that explain previous observations of eclipses which 

 seemed to invalidate the existence of the corona as a gaseous 

 incandescent medium. On the whole, the observations of the 

 5th of April, 1875, have advanced us a fresh step in the know- 

 ledge of the corona by bringing forward new proofs of the 

 existence of an atmosphere round the sun, principally gaseous, 

 incandescent, and very extended. 



In his second paper Dr. Janssen stated the results obtained by 

 the expedition to Japan to observe the Transit of Venus. The 

 expedition, which was under Dr. Janssen's direction, divided into 

 two parts, the one taking up its station at Nagasaki and the 

 other at Kobi. At Nagasaki Dr. Janssen observed the transit 

 with an equatoreal of 8 inches aperture. (l) He obtained the 

 two interior contacts. (2) He saw none of the phenomena of the 

 drop or of the ligament ; all the appearances were geometrical. 

 (3) He observed facts which establish the existence of an atmo- 

 sphere to Venus. (4) He saw the planet Venus before her entry 

 on the sun, with suitable coloured glasses. This important ob- 

 servation proves the existence of the coronal atmosphere. {5) 

 There was taken at Nagasaki a plate of the revolver for the first 

 interior contact. (6) M. Tisserand observed the two interior 

 contacts with a 6-inch equatorial ; the contacts were sensibly 

 geometrical. (7) Sixty photographs of the transit on silvered 

 plates were obtained ; and (8) also some other photographs (wet 

 collodion and albumenised glass). At Kobi (weather magnifi- 

 cent) fifteen good photographs of the transit (wet collodion and 

 albumenised glass) were obtained of about 4 inches in size ; they 

 will admit of being combined with the English photographs at 

 the southern stations. The astronomical observation of the 

 transit was successfully made by M. De la Croix, who was pro- 

 vided with a 6.inch telescope. His observations attest the 

 existence of an atmosphere round Venus. 



Dr. Janssen's third communication related to his magnetic 

 observations in the Gulf of Siam and the Gulf of Bengal. He 

 made observations at Bangkok, Bangchallo, Ligor, Singora, and 

 Singapore, and concluded that the magnetic equator passes 

 actually between Ligor and Singora, about 7° 43' N. latitude. 

 The line without declination passes very near to Singapore. In 

 the Gulf of Bengal the equator passes through the north of 

 Ceylon (the precise position will be given). The position of 

 Ligor has been rectified. It is erroneously placed on the maps 

 lat. 8" 24' 30", 



Dr. Janssen had also made some observations which relate to 

 mirage at sea. He had paid great attention to the phenomena 

 in all his journeys since 1868, and had observed some very 

 curious fads relating to mirage chiefly at sunrise and sunset. 

 He found that (l) the mirage was almost constant at the surface 

 of the sea ; (2) that the appearances were exphii led by admitting 

 the existence of a plane of total reflection at a certain height 

 above the sea ; (3) that the phenomena are due to a thermic and 

 hygrometric action of the sea on the neighbouring atmospheric 

 strata ; (4) that there exist at sea direct, inverse, lateral, and 

 other mirages ; (5) that the phenomena have a very general in- 

 fluence on the apparent height of the sea horizon, which is some- 

 limes diminished, sometimes increased. This variation of the 

 apparent horizon it is very important to take into account, if we 

 remember the use made of the horizon in nautical astronomy. 



Prof. Hennessy, of Dublin, read two papers, one On the in- 

 fluence of the physical properties of water on climate, and the 

 other On the possible influence on climate of the substitution of 

 water for land in Central and Northern Africa. In the former 

 the author referred to his earlier writings, in which he had taken 

 an opposite view to Sir John Herschel, who stated that the 

 effect of land under sunshine was to throw heat into the general 



atmosphere, and to distribute it by the carrying power of the air 

 over the whole earth, and that water was much less effective in 

 this respect, the heat penetrating its depths and being there ab- 

 sorbed, so that the surface never acquires a very elevated tempera- 

 ture even under the equator. I'rof. Hennessy had arrived at 

 the conclusion that of all substances largely existing in nature, 

 water was that which was the most favourable to the absorption 

 and distribution of solar heat throughout the external coating 

 of the earth. 



In his second paper, the author referred to'the fact that more 

 than six years since he had put forward proofs of the connection 

 between some of the hot winds that blow from the south-west in 

 Central and Southern Europe with the currents of the Atlantic, 

 and not with the Desert of Sahara, as has been usually supposed. 

 Similar views had been enunciated by Prof. Wild, director of 

 the Physical Observatory of Russia, and others. The attention 

 excited by the great midday heat of Central Africa caused many to 

 overlook the remarkably low nocturnal temperature, and thus to 

 ascribe to the desert a thermal influence that it does not possess. 

 The author's views with regard to the physical properties of 

 water in connection with climate, indicate that the substitution 

 of an area of water over the Sahara for the existing dry land 

 would be followed by the storing up of the heat received so 

 largely in that region from the sun's rays which is now partly 

 dissipated by nocturnal radiation. A great mediterranean sea 

 in Africa would become a source of positive thermal influence on 

 distant places. In the Red Sea the temperature is high by night 

 as well as by day, and this would also occur in the hypothetical 

 mediterranean of the Sahara. The climatal effect of this sea 

 would upon the whole result in a higher mean temperature for 

 the=e parts of the globe, and it would undoubtedly not operate 

 in producing a lower temperature in Europe so as to cause a 

 descent of the snow line. Its operation would probab'y be the 

 reverse. 



Prof. Osborne Reynolds read a paper On the Force caused by 

 the comjunnication 0/ Heat between a Surface and a Gas. — This 

 paper dealt chiefly with the remarkable discovery recently made 

 by Mr. Crookes, that, under certain conditions, discs of pith 

 suspended in a very perfect vacuum, and at the end of arms free 

 to rotate, are made to spin round when light or radiant heat falls 

 upon them. Prof. Reynolds said that he believed that Mr, 

 Crookes asserted that radiant heat was attended by a force which 

 produced this effect, but no such assumption would, he thought, 

 explain the results. When a candle was presented the disc 

 would tend to run away, and when a piece of ice was presented 

 it would tend to follow ; this showed that the force was not a radia- 

 tive one, and he thought that, except as regarded the raising of 

 the temperature of the body, radiant heat had nothing to do 

 with the motions. The suspended body might give up its heat 

 to the ether or to the surrounding gas, and thus propel itself, for 

 the communication of this heat to the surrounding medium must 

 be accompanied by a reaction. It had been said that Mr. Crookes 

 used a perfect vacuum, so that there could be no gaseous reac- 

 tion ; but it remained to be proved that he used a vacuum so 

 absolutely perfect. The greater the perfection of the vacuum 

 the less was the resistance, and that was why the body appeared 

 under such circumstances to be driven by a greater force. He 

 had not witnessed the experiments Lwith light, made by Mr. 

 Crookes, but he thought that the results were probably due to 

 the conversion of light into heat. — The discussion on this paper 

 was adjourned, as it was hoped that Mr, Crookes would be able 

 to be present ; unfortunately, however, he was not able to 

 arrive in time, and Prof. Balfour Stewart, the president, re- 

 marked that, as had been said by Prof. Stokes, it was doubtful 

 whether Prof. Reynolds's explanation covered the whole ground. 

 There was something else besides residual gas in the bulbs, viz., 

 ether, and the particles of the radiometer might communicate 

 more force to the ether when moving in one direction than when 

 Jailing back again ; consequently, motion might be given to the 

 whole body to restore the balance. At all events Mr. Crookes's 

 experiments were among the most interesting in the range of 

 physical science. 



Capt. H. Toynbee read a paper On the physical geography oj 

 that part of the Atlantic Doldrums which lies in the track oj 

 ships crossing the Equator. The paper was accompanied by 

 diagrams, which showed the isobaric lines of mean pressure for 

 each -05 of an inch, together with arrows showing the prevailing 

 winds and their force, also the isothermal lines for every second 

 degree of air temperature, and further the isothermal lines for 

 every second degree of sea temperature, together with arrows 

 showing the prevailing currents and their speed in twenty-four 



