394 



NATURE 



[Sept. 7, 1876 



built up the two great branches of knowledge with which their 

 names will always be inseparably connected. It was here that 

 Dr. Thomas Thomson established the first school of Practical 

 Chemistry in Great Britain, and that Sir W. Hooker gave to the 

 chair of Botany a European celebrity ; it was here that Graham 

 discovered the law of gaseous diffusion and the properties of 

 polybasic acids ; it was here that Stenhouse and Anderson, 

 Rankine and J. Thomson made some of their finest discoveries ; 

 and it was heie that Sir William Thomson conducted his phy- 

 sico-mathematical investigations, and invented those exquisite 

 instruments, valuable alike for ocean telegraphy and for scientific 

 use, which are among the finest trophies of recent science. Nor 

 must the names ot Tennant, Mackintosh, Neilson, Walter 

 Crum, Young, and Napier be omitted, who, with many others 

 in this place, have made large and valuable additions to practical 

 science. 



The safe return of the Challenger, after an absence of three 

 and a half years, is a subject of general congratulation. Our 

 knowledge of the varied forms of animal life, and of the remains 

 of animal life, which occur, it is now known, over large tracts of 

 the bed of the ocean, is chiefly derived from the observations 

 made in the Challenger and in the previous deep-sea expeditions 

 which were organised by Sir Wyville Thomson and Dr. Car-, 

 penter. The physical observations, and especially those on the 

 temperature of the ocean, which were systematically conducted 

 throughout the whole voyage of the Challenger, have already 

 supplied valuable data for the resolution of the great question of 

 ocean-currents. Upon this question, which has been discussed 

 with singular ability, but under different aspects, by Dr. Car- 

 penter and Mr. Croll, I cannot attempt here to enter ; nor will 

 1 venture to forestall, by any crude analysis of my own, the nar- 

 rative which Sir W. Thomson has kindly undertaken to give of 

 his own achievements and of those of his staff during their long 

 scientific cruise. 



Another expedition, which has more than fulfilled the expec- 

 tations of the public, is Lieut. Cameron's remarkable journey 

 across the continent of Africa. It is by such enterprises, happily^ 

 conceived and ably executed, that we may hope at no distant day 

 to see the Arab slave-dealer replaced by the legitimate trader, 

 and the depressed populations of Africa gradually brought within 

 the pale of civilised life. 



From the North Polar Expedition no intelligence has been 

 received ; nor can we expect for some time to hear whether it 

 has succeeded in the crowning object of Arctic enterprise. In 

 the opmion of many, the results, scientific or other, to be gained 

 by a full survey of the Arctic regions can never be of such value 

 as to justify the risk and cost which must be incurred. But it is 

 not by cold calculations of this kind that great discoveries are 

 made or great enterprises achieved. There is an inward and 

 irrepressible impulse— in individuals called a spirit of adventure, 

 in nations a spirit of enterprise — which impels mankind forward 

 to explore every part of the world we inhabit, however inhos- 

 pitable or difficult of access ; and if the country claiming the 

 foremost place among maritime nations shrink from an under- 

 taking because it is perilous, other countries will not be slow to 

 seize the post of honour. If it be possible for man to reach the 

 poles of the earth, whether north or south, the feat must sooner 

 or later be accomplished ; and the country of the successful ad- 

 venturers will be thereb* raised in the scale of nations. 



The passage of Venus over the sun's disc is an event which 

 cannot be passed over without notice, although many of the cir- 

 cumstances connected with it have already become historical. It 

 'was to observe this rare astronomical phenomenon, on the occa- 

 sion of its former occurrence in 1 769, that Capt. Cook's memo- 

 rable voyage to the Pacific was undertaken, in the course of 

 which he explored the coast of New South Wales, and added 

 that great country to the possessions of the British Crown. 



As the transit of Venus gives the most exact method of calcu- 

 lating the distance of the earth from the sun, extensive prepara- 

 tions were made on the last occasion for observing it at selected 

 stations — from Siberia in northern, to Kerguelen's Land in 

 southern latitudes. The great maritime powers vied with each 

 other to turn the opportunity to the best account ; and Lord 

 Lindsay had the spirit to equip, at his own expense, the most 

 complete expedition which left the shores of this country. Some 

 of the most valuable stations in southern latitudes were desert 

 islands, rarely free from mist or tempest, and without harbours 

 or shelter of any kind. 1 he landing of the instruments was in 

 many cases attended with great difficulty and even personal risk. 

 Photography lent its aid to record automatically the progress of 



the transit ; and M. Janssen contrived a revolving plate, by 

 means of which from fifty to sixty images of the edge of the sun 

 could be taken at short intervals during the critical periods of 

 the phenomenon. 



The observations of M. Janssen at Nagasaki, in Japan, were 

 of special interest. Looking through a violet-blue glass he saw 

 Venus, two or three minutes before the transit began, having the 

 appearance of a pale round spot near the edge of the sun. Im- 

 mediately after contact the segment of the planet's disc, as seen 

 on the face of the sun, formed with what remained of this spot a 

 complete circle. The pale spot when first seen was, in short, a 

 partial eclipse of the solar corona, which was thus proved beyond 

 dispute to be a luminous atmosphere surrounding the sun. Indi- 

 cations were at the san-e time obtained of the existence of an 

 atmosphere around Venus. 



The mean distance of the earth from the sun was long supposed 

 to have been fixed within a very small limit of error at about 

 95,000,000 miles. The accuracy of this number had already 

 been called in question on theoretical grounds by Hansen and 

 Leveirier, when Foucault, in 1862, decided the question by an 

 experiment of extraordinary delicacy. Taking advantage of the 

 revolving-mirror, with which Wheatstone had some time before 

 enriched the physical sciences, Foucault succeeded in measuring 

 the absolute velocity of light in space by experiments on a beam 

 of light, reflected backwards and forwards, within a tube little 

 more than thirteen feet in length. Combining the result thus 

 obtained with what is called by astronomers the constant of 

 aberration, Foucault calculated the distance of the earth from the 

 sun, and found it to be one-thirtieth part, or about 3,000 000 

 miles, less than the commonly received number. This conclu- 

 sion has lately been confirmed by M. Cornu, from a new deter- 

 mination he has made of the velocity of light according to the 

 method of Fizeau ; and in complete accordance with these results 

 are the investigations of Leverrier, founded on a comparison with 

 theory of the observed motions of the sun and of the planets 

 Venus and Mars. It remains to be seen whether the recent 

 observations of the transit of Venus, when reduced, will be suffi- 

 ciently concordant to fix with even greater precision the true 

 distance of the earth from the sun. 



In this brief reference to one of the finest results of modern 

 science, I have mentioned a great name whose loss England has 

 recently had to deplore, and in connection with it the name of 

 an illustrious physicist whose premature death deprived France, 

 a few years ago, of one of her brightest ornaments — Wheatstone 

 and Foucault, ever to be remembered for their marvellous power 

 of eliciting, like Galileo and Newton, from familiar phenomena 

 the highest truths of nature ! 



The discovery of Huggins that some of the fixed stars are 

 moving towards and others receding from our system, has been 

 fully confirmed by a careful series of observations lately made by 

 Mr. Christie in the Observatory of Greenwich. Mr. Huggins 

 has not been able to discover any indications of a proper motion 

 in the nebulae ; but this may arise from the motion of translation 

 being less than the method would discover. Few achievements 

 in the history of science are more wonderful than the measure- 

 ment of the proper motions of the fixed stars, from observing the 

 relative podtion of two delicate lines of light in the field of the 

 telescope. 



The observation of the American astronomer Young, that 

 bright lines, corresponding to the ordinary lines of Fraunhofer 

 reversed, may be seen in the lower strata of the solar atmosphere 

 for a few moments during a total eclipse, has been confirmed by 

 Mr. Stone, on the occasion of the total eclipse of the sun which 

 occurred some time ago in South Africa. In the outer corona, 

 or higher regions of the sun's atmosphere, a single green line 

 only was seen, the same which had been already described by. 

 Young. 



I can here refer only in general terms to the observations of 

 Roscoe and Schuster on the absorption-bands of potassium and 

 sodium, and to the investigations of Lockyer on the absorptive 

 powers of metallic and metalloidal vapours at different tempera- 

 tures. From the vapour of calcium the latter has obtained two 

 wholly distinct spectra, one belonging to a low, and the other to 

 a high, temperature. Mr. Lockyer is also engaged on a new 

 and greatly extended map of the solar spectrum. 



Spectrum analysis has lately led to the discovery of a new metal 

 — gallium — the fifth whose presence has been first indicated by 

 that powerful agent. This discovery is due to M. I-ecoq de 

 Boisbaudran, already favourably known by a work on the appli- 

 cation of the spectroscope to chemical analysis. _ 



