346 



NATURE 



{Ang: 26, 1875 



attaching the muzzle of the gun to an outer casing, through which 

 the force of the recoil is carried back to the trunnions, he pro- 

 poses to avail himself of this elasticity to the extent of one-and- 

 a-half times the length of the gun ; whether its elasticity alone 

 in so short a space will suffice without aid is, perhap'', doubtful ; 

 but other aid may be applied, and the experiment, whether suc- 

 cessful or not, will be interesting. 



Docks and harbours I have no time to mention, for it is time 

 this long and, I fear, tedious address, should close. 



" Whence and whither," is an aphorism which leads us away 

 from present and plainer objects to those which are more distant 

 and obscure ; whether we look backwards or forwards, our vision 

 is speedily arrested by an impenetrable veil. 



On the subjects I have chosen you will probably think I have 

 travelled backwards far enough. I have dealt to some extent 

 with the present. 



The retrospect, however, may be useful to show what great 

 works were done in former ages. 



Some things have been better done than in those earlier times, 

 but not all. 



In what we choose to call the ideal we do not surpass the 

 ancients. Poets and painters and sculptors were as great in 

 former times as now ; so, probably, were the mathematicians. 



In what depends on the accumulation of experience, we ought 

 to excel our forerunners. Engineering depends largely on expe- 

 rience ; nevertheless, in future times, whenever difficulties shall 

 arise or works have to be accomplished for which there is no 

 precedent, he who has to perform the duty may step iorth from 

 any of the walks of life, as engineers have not unfrequently 

 hitherto done. 



The marvellous progress of the last two generations should 

 make everyone cautious of predicting the future. Of engineering 

 works, however, it may b^ said that their practicability or im- 

 practicability is often determined by other elements than the 

 inherent difficulty in the works themselves. Greater works than 

 any yet achieved remain to be accomplished — not perhaps yet 

 awhile. Society may not yet require them ; the world could not 

 at present afford to pay for them. 



The progress of engineering works, if we consider it, and the 

 expenditure upon them, has already in our time been prodigious. 

 One hundred and sixty thousand miles of railway alone, put into 

 figures at 20,000/. a mile, amounts to 3,200 million pounds 

 sterling ; add 400,000 miles of telegraph at 100/. a mile, and 

 100 millions more for sea canals, docks, harbours, water and 

 sanitary works constructed in the same period, and we get the 

 enormous sum of 3,340 millions sterling expended in one gene- 

 ration and a half on what may undoubtedly be called useful 

 works. 



The wealth of nations may be impaired by expenditure on 

 luxuries and war ; it cannot be diminished by expenditure on 

 works like these. 



As to the future, we know we cannot create a force ; we can, 

 and no doubt shall, greatly improve the application of those 

 with which we are acquainted. What are called inventions can 

 do no more than this, yet how much every day is being done by 

 new machines and instruments. 



The telescope extended our vision to distant worlds. The 

 spectroscope has far outstripped that instrument, by extending 

 our powers of analysis to regions as remote. 



Postal deliveries were and are great and able organisations, 

 but what are they to the telegraph ? 



Need we try to extend our vision into futurity farther ? Our 

 present knowledge, compared to what is unknown even in 

 phyiics, is infinitesimal. We may never discover a new force — 

 yet, who can tell ? 



SECTION A. 



Mathematical and Physical. 



Opening Adbress by the President, Prof. Balfour 



Stewart. 



Since the last meeting of the British Association, science has 



had to mourn the loss of one of its pioneers, in the dcTth of the 



veteran astronomer, Schwabe, of Dessau, at a good old age, not 



before he had faithlully and horourably finished his work. In 



truth this work was of such a nature that the worker could 



not be expected long to survive its completion. 



It is now nearly fifty years since he fint began to produce 

 daily sketches of the spots that appeared upon the sun's sur''ace. 

 Everyday on which the sun was visible (and such days are more 



frequent in Germany than in this country), with hardly any inter- 

 mission for forty years, this laborious and venerable observer 

 made his sketch of the solar di?c. At length this unexampled 

 perseverance met with its reward in the discovery of the perio- 

 dicity of sun-spots, a phenomenon which very speedily attracted 

 the attention of the scientific world. 



It is not easy to over-rate the importance of the step gained 

 when a periodicity was found to rule th^se solar outbreaks. A 

 priori we should not have expected such a phenomenon. If the 

 old astronomers were perplexed by the discovery of sun-spots, 

 their successors must have been equally perplexed when they 

 ascertained their periodicity. For while all are reaty to acknow- 

 ledge periodicity as one of the natural conditions of terrestrial 

 phenomena, yet everyone is inclined to ask what there can be to 

 cause it in the behaviour of the sun himself. Manifesily it can 

 only have two possible causes. It must either be the outcome 

 of some strangely hidden periodical cause residing in the sun 

 hiinself, or must be produced by external bodies, such as planets, 

 acting somehow in their varied positions on the atmosphere of 

 the sun. But whether the cause be an internal or external one — 

 in either case we are completely ignorant of its nature. 



We can easily enough imagine a cause operating from the 

 sun himself and his relations with a surrounding medium to pro- 

 duce great disturbances on his surface, but we cannot easily 

 imagine why disturbances so caused should have a periodicity. 

 On the other hand we can easily enough attach periodicity to 

 any efTect caused by the planets, but we cannot well see why 

 bodies comparatively so insignificant shouM contribute to such 

 very violent outbreaks as we now know sun-spots to be. 



If we look within we are at a loss to account for the periodicity 

 of solar disturbances, and if we look without we are equally at a 

 loss to account for their magnitude. Bat since that within the 

 sun is hidden from our view, it cinnot surely be considered 

 blameworthy if astronomers have directed their attention to thit 

 without and have endeavoured to connect the behaviour of sun- 

 spots with the positions of the various planets. Stimulated no 

 doubt by the success which had attended the labours o' Schwabe, 

 an English astronomer was the next to enter the field of solar 

 research. 



The aim of Mr. Carrington was, however, rather to obtain 

 very accurnte records of the positions, the sizes, and the shapes 

 of the various sun-spots than to make a very extensive and long- 

 continued series of observations. He was aware that a series 

 at once ver}' accurate and very extended is beyond the power of 

 a private individual, and can only be undertaken by an estab- 

 lished institution. Nevertheless, each sun-spot that made its 

 appearance during the seven years extending from the beginning 

 of 1854 to the end of i860 was sketched by Mr. Carrington with 

 the greatest possible accuracy, and had also its heliographic 

 position, that is to say its solar latitude and longitude, accurately 

 determined. 



One of the most prominent results of Mr. Carrington's labiurs 

 was the discovery of the fact that sun-spots appear to have a 

 proper motion of their own — those nearer the solar equaor 

 moving faster than those more remote. Another was the dis- 

 covery of changes apparently periodical affecting tl e disposition 

 of spots in solar latitude. It was already known that sun-spots 

 confined themselves to the sun's equatorial regions, but Mr. 

 Carrington showed that the region affected was lia'^-le to perio- 

 dical elongations and contractions, although his observations 

 were not 'sufficiently extended to determine the exact length of 

 this period. 



Before Mr. Carrington had completed his seven' years labours, 

 celestial photognphy had been introduced by Mr. Warren De 

 la Rue, Commencing with his private observatory, he next 

 persuaded the Kew Committee of the British Association to 

 allow the systematic photography of the sun to be carried on at 

 their observatory under his superintendence, and in the year 1862 

 the first of a ten years' series of solar photographs was begun. 

 Before this date however Mr. De la Rue had ascertained, by 

 means of his phot^oheliograph, on the occasion of the total 

 eclipse of i860, that the red prominences surroun/iing the 

 eclipsed sun, belong, without doubt, to our luminary himself. 



The Kew observations are not yet finally reduced, but already 

 several important conclusions have been obtained from them by 

 Mr. De la Rue and the other Kew observers. In the first 

 place the Kew photographs confirm the theory of Wilson that 

 sun-spots are phenomena, the dark portions of which exist at a 

 level considerably beneath the general surface of the sun ; in other 

 words, they are hollows, or pits, the interior of which is of course 

 filled up with the solar atmosphere. The Kew observers were 



