Dec. 2, 1886] 



NA TURE 



117 



may be mentioned his determination of the condiictinij powers 

 of metals for heat by a method which appears to possess special 

 advantages, and his investigation of the effect of extremely great 

 pressures on thermometers, undertaken with a view to deducing 

 correct results for the temperatures at great depths in the ocean 

 from the observati ins made in the ChaUeni;er expedition. This 

 latter subject has led him to investigate the behaviour, as to 

 couiprc^sibility and development of heat, of liquids and solids 

 under enormous pressures, a subject in which he is still engaged. 

 Before concluding, I must mention his elaborate papers on systems 

 of knots, recently printed in the Ttansaclions of the Royal 

 Society of Edinburgh. 



The other Royal Medal has been awarded to our Fellow, 

 Mr. Francis Galton, for his statistical inquiries into biological 

 phenomena. 



Mr. Galton is well known as an explorer and geographer, and 

 his mind is singularly fertile in the devising of ingenious instru- 

 ments for various objects. Many years ago he brought before us 

 some remarkable experiments instituted with a view to test a 

 particular biological theory, in which rabbits of a pure variety 

 were so connected with others of a different variety that the same 

 blood circulated through both individuals, and the point to deter- 

 mine was whether this blood-relationship, in the most literal 

 sense of the term, had any effect on the offspring. Contrary to 

 what the theory in question led us to regard as the more probable, 

 the result proved to be negative. It is, however, in accordance 

 with the rules for the award of the Royal Medals, more espe- 

 cially the later investigations of Mr. Galton, in relation to vital 

 statistics, that have been taken as the ground of the award. He 

 has shown that by taking the average of a number of individuals 

 having some condition in common, individual peculiarities apart 

 from that condition are eliminated in the mean, and results are 

 obtained which may be regarded as typical of that condition. 

 One way of doing this is by his method of compound photo- 

 graphs. Thus we may obtain typical features of criminals of a 

 particular kind, of consumptive persons, and so forth. By 

 adhering to the method of averages, he has even succeeded in 

 obtaining a mathematical expression, very closely verified in 

 observation, connecting the mean deviation of some condition 

 (such for example as stature) in a series of individuals, from the 

 general mean of the same condition, with the mean deviations of 

 the same condition in the relatives of tho^e same individuals of 

 different kinds, such ai fathers, brothers, &c. Nor is the statis- 

 tical method applicable to bodily characteristics alone. Mr. Galton 

 has even extended it with remarkable ingenuity and originality 

 to mental phenomena also. 



The Rumford Medal has been awarded to Prof. Samuel P. 

 I^angley, for his researches on the spectrum by means of the 

 bolometer. 



A better knowledge of the ultra-red region of the spectrum, 

 which includes the larger part of the energy of solar radiation, 

 liad loi'g been a desideratum when Prof. Langley commenced 

 his work upon this subject. Finding the thermopile insufficiently 

 sensitive for his purpose, he contrived the "bolometer." This 

 instrument depends upon the effect of temperature upon the 

 electrical resistance of metals, a quantity suscej>tible of very 

 accurate measurement ; and, with its aid, Prof. Langley has been 

 .able to explore a part of the spectrum previously almost inac- 

 cessible to observation. 



A result of Prof. Langley's work, vei7 important from the 

 point of view of optical theory and of the ultimate constitution 

 iif matter, relates to the law of dispersion, or the dependence 

 of refrargibility on wave-length. Cauchy's formula, which 

 corresponds well with observation over most of the visible spec- 

 trum, is found to break down entirely when applied to the extreme 

 ultra- red. 



Prof. Langley has given much attention to the important 

 question of the influence of the atmosphere on solar radiation. 

 The expedition to Mount Whitney, successfully conducted by 

 him in face of many difficulties, has given results of the utmost 

 value, pointing to conclusions of great interest and novelty. 



The Davy Medal has been awarded to our Foreign Member, 

 M. Jean Charles Galissard de Marignac, for his researches on 

 atomic weights. 



M. Mangnac's numerous researches on atomic weights, which 

 have been continued for a great number of years, have played 

 an exceedingly important part in establishing and consolidating 

 that ground-work of chemistry. They are remarkable for ori- 

 ginality in devising methods appropriate to the respective cases, 

 the most conscientious care in discovering errors which occurred 



in the respective operations, and indefatigable perseverance in 

 finding means to eliminate the disturbing influences. His labours 

 are all the more valuable because he chose for their field chiefly 

 those elements which are most generally used in chemistry, and 

 are most important to chemists, and on which the determination 

 of new atomic weights is most generally made to depend. 



TE.\- YEARS' PROGRESS IN ASTRONOMY^ 



in. 



r'OMETS. — During the past ten years we have been favoured 

 with an extraordinary number of comets, and while perhaps 

 no single great step has been made, yet it is certain, I think, 

 that our knowledge of these mysterious objects has gained a real 

 and considerable advance. 



In 1876, curiously enough, not a single comet appeared ; but 

 in 1877 there were 6 ; in 1S78, 3 ; in 1879, 5 ; in 18 o, 5 ; in 

 1881, S ; in 1882, 3 ; in 1883, 2 ; in 1S84, 3 ; and in 1885, 6 ; 

 and so far this year, 3. Forty-four comets in all have been 

 observed during the ten years, six of which were conspicuous 

 objects to the naked eye, and two of them, the great comet of 

 1881, and the still greater one of 1882, were very remarkable 

 ones. 



The first of these will always be memorable as the first comet 

 ever photographed. Dr. Henry Draper photographed both the 

 comet itself and its spectrum ; Janssen obtained a picture of the 

 comet, and Huggins of its spectrum. 



A number of excellent photographs were obtained of the 

 great comet of 18S2, especially by Gill, at the Cape. And it is 

 worth mentioning that in May 1882 a little comet (not included 

 in the preceding list, because no observations were obtained of 

 it) was caught upon the photographs of the Egyptian eclipse. 



Two of the bright comets, Wells's comet of 1S81 and the great 

 comet of 1882, approached very close to the sun, and their 

 spectra, as a consequence, became very complex and interesting. 

 A great number of bright lines made their appearance. Sodium 

 was readily and certainly recognised ; iron and calcium pro- 

 bably, but not so surely. The evidence as to the nature of the 

 sun's corona, derived from the swift passage of the l8Sl comet 

 through the coronal regions, has already been alluded to. 



The Pons-Brooks comet of 1883-84 is extremely interesting 

 as presenting the first instance (excepting Halley's comet, of 

 course) of one of the Neptunian family of comets returning to 

 perihelion. There are six of these bodies with periods ranging 

 from sixty-eight to seventy years. Halley's comet, the only 

 large one of the group, has made irany returns, and is due in 

 1910. Pons's comet, first observed in l8i2, has now returned ; 

 Olbers's comet of 1815 is due in 1889, and the three others, all 

 of them small, in 1919-20 and 1922. 



I have spoken of them as Neptunian comets, i.e. their pre- 

 sence in our system is known to be due in some way to this 

 planet. The now generally received theory is that they have 

 had their orbits changed from parabolas into their present shape 

 by I he disturbing action of Neptune. Mr. Proctor has pointed 

 out certain unquestionable, though, I think, inconclusive, ob- 

 jections to this view, and he proposes, as an alternative, the 

 startling and apparently improbable hypothesis, that they have 

 been ejected from the planet at some past time by something like 

 volcanic action. 



On the whole, however, the most important work relating to 

 comets has been that of the Russian astronomer Bredichin. He 

 has brought the mechanical and mathematical portion of the 

 theory of comet's tails to a high degree of perfection ; following 

 out the lines laid down by Bessel, but improving and correcting 

 Bessel's formulEe, and determining their constants by a most 

 thorough discussion of all the accurate observations available. 



It is hardly pos-ible to doubt any longer that all the facts can 

 be represented on the hypothesis that the tails are composed of 

 minute particles of matter, first driven off by the comet, and then 

 repelled by the sun. Bredichin's most interesting result, arrived 

 at in 1878, is that the tails appe.ar to be of three, and only three, 

 distinct types — the long straight streamers which are due to a 

 repulsive acceleration about twelve times as great as the sun's 

 attraction ; the seconti and most ordinary class of broad-curved 

 tails for which the repulsive force ranges between one and two 

 and a half times that of the attraction ; and, finally, the short, 



' -'IVn Year 

 Read May 17, i 

 from p. 98. 



rogress in Astronomy, 1876-86," by Prof. C. A. Young. 

 , before the New York Academy of Sciences. Continued 



