Dec. 5, 1878] 



NATURE 



I II 



research, or awakening attention to hitherto unseen or unre- 

 cognised, or unexplained phenomena of nature. 



In the foremost rank as regards the magnitude of the under- 

 takings and the combination of means to carry them out, nothing 

 in the history of physical science can compare with the Transit 

 of Venus Expeditions. To observe the transit of Veaus various 

 nations of Europe and the United States competed as to the 

 completeness of the expeditions they severally equipped. The 

 value ^ of the solar parallax cannot be ascertained until the re- 

 sults of all the expeditions are taken into account, when it will 

 have an international claim to acceptance. But ad\-ances in this 

 direction will not have ended here, the very difficulties attending 

 the observation of the transit of Venus, having directed attention 

 to the method originally su^ested by the Astronomer- Royal in 

 1857, of obtaining the solar parallax from the diurnal parallax 

 of Mars at its opposition. 



Mr. Gill, by the skilful employment at Ascension Island of 

 the heliometer lent by Lord Lindsay, has greatly increased the 

 accuracy of the method by which the necessary star comparisons 

 with Mars are made, and there is every reason to believe that 

 the results of his observations, which are now in course of re- 

 daction, will be very satisfactor}'. 



Within the last two years a remarkable addition has been 

 made to the number of members of the solar system by Prof. 

 Asaph Hall's discovery of the satellites of Mars ; and more re- 

 cently, during the solar eclipse which was visible in America, by 

 Prof. Watson's detection of planetary bodies within the orbit of 

 mercurj'. 



In 1876 Schmidt recorded an outburst of light in a star in 

 Cygnus, which showed a continuous spectrum containing bright 

 lines similar to those of the remarkable star of 1866. As the 

 star waned the continuous spectrum and bright lines faded, all 

 but one bright line in the green, giving the object the spectrosco- 

 pic appearance of a small gaseous nebula. 



Great progress has been made during the last five yeai^ at 

 Greenwich in the method of determining the motions of the 

 heavenly bodies by the displacement of the line^ in their spectra, 

 as first successfully accomplished by Mr. Huggins in 1868. Not 

 only do the results obtained by the stars observed at Greenwich 

 agree with those of Mr. Hu;^ins, as satisfactorily as can be 

 expected in so delicate an investigation, but the motions of 

 seventeen more have been determined ; whilst the trustworthi- 

 ness of the method has been shown by the agreement of the 

 values for the rotation of the sun and the motions of Venus, 

 with the known movements of these bodies. Mr. Huggins has 

 also obtained photographs of the spectra of some of the brighter 

 stars, which give well-defined lines in the violet and ultra-violet 

 parts of the spectrum. These spectra have already shown 

 alterations in the lines common to them and the sun, which are 

 of much interest. 



In solar physics, which afford remarkable evidence of Mr. 

 Lockyer's energetic labours in this countrj- and Mr. Tanssen's in 

 France, I must mention our Foreign Member's wonderful photo- 

 graphs of the sun, wherein the minutest of the constant changes 

 in the granulations exhibited on its surface (and which vary in 

 size from yV of ^ second to 3 or 4 seconds) can be studied in the 

 future from hour to hour and day to day ; as can also their 

 different behaviour at different periods of fi-equency of sun- 

 spots. 



Before dismissing this fruitful field of research, I must allude 

 to Mr. Lockyer's discovery of carbon in the sun ; and to his 

 announced but not yet published observations on the changes 

 and modifications of spectra under different conditions, some 

 of which he even regards as indicating the breaking up of the 

 atoms of bodies hitherto regarded as elementary. 



Some important investigations on the electric discharge have 

 been communicated to the Society by Messrs. De La Rue and 

 Miiller, and by Mr. Spottiswoode. These, prosecuted by 

 different means, tend to limit the possible causes of the stratifi- 

 cation observed in discharges through vacuum tubes. They also 

 point to the conclusion that this phenomenon is in a great 

 measure due to motions among the molecules of the residual 

 gas which themselves become vehicles for the transmission 

 of electricity through the tube. It is weU known that gases 



« The Astrcnomer-Royal informs me that Capt. Tupman. who has takea 

 tne FnnciFal share m the supenntendcnce of *he calculation, fixes pro- 

 visionally on a mean parallax of 8" -8455. corresponding to a distance of 

 52.400,000 Br t.sh miles, but that the obsenations would be fairiy satUfied 

 *y any parallax between 8"-82 and 8"-83, which io distance produces a 

 r^n^n?! 1 92.°*4,ooo and 92.770,000 miles, differing by 726,000 miles, 

 a quaat.ty ahaost equal to the sun s d.ameter. 



at atmospheric pressure offer great resistance to the passage of 

 electricity ; and that this resistance diminishes (to a certain 

 limit, different for different gases) with the presstire. And the 

 researches in question appear to show that the discharge, mani- 

 festly disruptive at the higher pressures, is really also disruptive 

 even at pressures when stratification takes place. The period 

 of these discontinuous discharges has not yet been the subject of 

 measurement, but it must, in any case, be of a very high order . 



Under the auspices of the Elder Brethren of the Trinity House, 

 and as their scientific adviser. Prof. Tyndall has conducted an 

 investigation on the acoustic properties of the atmosphere. The 

 instruments employed included steam whistles, trumpets, steam 

 syrens, and guns. The propagation of sound through fog 

 was proved to depend not upon the suspended aqueous [>articles, 

 but upon the condition of the sustaining air. And as air of 

 great homogeneity is the usual associate of fog, such a medium 

 is often astonishingly transparent to sound. Hail, rain, snow, 

 and ordinary misty weather, were also proved to offer no sensible 

 obstruction to the passage of sound. Every [phenomenon ob- 

 served upon the large scale was afterwards reproduced experi- 

 mentally. Clouds, fumes, and artificial showers of rain, hail, 

 and snow- were proved quite ineffectual to stop the sound, so 

 long as the air was homogeneous, while the introduction of a 

 couple of burners into a space filled with acoustically transparent 

 air soon rendered it impervious to the waves of sound. As long 

 as the continuity of the air in their interstices was preserved, the 

 sound-waves passed freely through silk, flannel, green baize, 

 even through masses of hard felt half an inch in thackness, the 

 same sound-waves being intercepted by goldbeater's skin. A 

 cambric handkerchief which, when dr>', offered no impediment 

 to their passage, when dipped into water became an impassable 

 barrier to the sound-waves. 



Echoes of extraordinary intensity were sent back from non- 

 homogeneous transparent air ; while similar echoes were after- 

 wards obtained from the air of the laboratory, rendered non- 

 homogeneous by artificial means. Detached masses of non- 

 homogeneous air often drift through the atmosphere, as clouds 

 pass over the face of the sky. This has been proved by the 

 fluctuations obser\'ed with bells having their clappers adjusted 

 mechanically, so as to give a uniform stroke. The fluctuations 

 occiir only on certain days ; they occtir when care has been 

 taken to perfectly damp the bell between every two succeeding 

 strokes ; and they also occur when the direction of the sound is 

 at right angles to that of the wind. Numerous observations 

 were also naiade on the influence of the wind, the results obtained 

 by previous observers being thereby confirmed. From his own 

 observations, as well as from the antecedent ones of Mr. 

 Alexander Beazeley and Prof. Osborne Reynolds, Prof. Tyndall 

 concludes that the explanation of this phenomenon given by 

 Prof. Stokes is the true one. 



Turning now to biological branches of science, I find that the 

 discoveries and researches of the past five years in this department 

 also are far in advance of those of any previous period of equal 

 length. The Challenger Expedition was, in point of the 

 magnitude of the undertaking and completeness of its equipment, 

 the rival of that for obser\-ing the Transit of Ventis. Its general 

 results, as far as hitherto made known, have been dwelt upon at 

 length in my previous addresses, and the publication of them in 

 detail is being rapidly pushed forward. Some very important 

 papers by Mr. Moseley on the corals collected on the voyage 

 have indeed been published in our Transactiotu with admirable 

 illustrations by himself. 



To the botanist and geologist no subject has a greater interest 

 than that of the conditions under which the successive floras, 

 which inhabited the polar area, existed and were successively 

 dispersed over lower latitudes previous to their extinction, some 

 in toto and over the whole globe, whilst others, though extinct 

 in the regions where they once flourished, exist now only in lower 

 latitudes under identical or under representative forms. It is only 

 during the last few years that, thanks to the labours of those en- 

 gaged in systematic botany in tracing accvirately the directions of 

 migrations of existing genera and species, and in determining the 

 affinities of the extinct ones, and of pabeontologists in referring 

 the latter to their respective geological horizons, that any material 

 advance has been made towards a knowledge of the origin and 

 distribution of earlier and later Floras. I caimot better illustrate 

 the condition of this inquiry than by calling your attention to 

 two most recent publications on the subject, which have both 

 appeared within the last few months. 



