Sept. 22, 1887] 



NATURE 



497 



the main statistics bearing on a particular point all indicate the 

 same conclusion, it is not difficult to reason from them and to 

 convince all who study them ; but when the indications are 

 apparently in conflict it would be folly to dogmatize. I have 

 indicated frankly my own opinion, but I, for one, should like the 

 subject to be more fully threshed out. It is a very obvious 

 suggestion, moreover, that one may prove too much by such figures 

 — that it is an outrage on common-sense to talk of there being no 

 check to the rate of growth in the country when times are notori- 

 ously bad and everybody is talking of want of profit. What I should 

 suggest finally, by way of a hypothesis reconciling all the facts, 

 would be that probably there is some check to the rate of material 

 growth in the last ten years, though not of the serious character 

 implied by the first set of figures discussed ; that this check may 

 even be too small to be measured by general statistics though it 

 is sufficient to account for no small amount of malaise ; and that 

 the malaise itself is largely accounted for, as I have suggested 

 on a former occasion, l)y the mere fall of prices, whatever the 

 cause, as it involves a great redistribution of wealth and income, 

 and makes very many people feel poorer, including many who 

 are not really poorer, but only seem so, and many who are really 

 richer if they only allowed properly for the increased purchasing 

 power of their wealth. All these facts are quite consistent with 

 the fact of a ver}' slight real diminution in the rate of our material 

 growth generally, and with that change in the direction of the 

 national industry, significant of a general change beginning 

 throughout the world which would seem to have occurred. 



To some extent also it ought to be allowed that the tendency 

 in the very latest years seems unsatisfactory, and that the de- 

 velopments of the next few years should be carefully watched. 

 Up to now there is nothing really alarming in the s.tatistics when 

 they are analyzed and compared. It may be the case, though I 

 do not think it is the case, that causes are in operation to pro- 

 duce that great check and retrogression which have not as yet 

 occurred, though many have talked as if they had occurred. The 

 exact limits of the discussion should be carefully kept in 

 mind. 



Fortunately, however, there is no doubt what some of the 

 conclusions on practical points should be. If it be the case that 

 the hold of an old country like England on certain staple in- 

 dustries of the world is less firm than it was, and, as I believe, 

 must be less and less firm from period to period, owing to the 

 natural development of foreign countries and the room there is 

 among ourselves for development in new directions, then we 

 should make assurance doubly sure that the country is really 

 developing in new directions. If our dependence must be on 

 the new advantages that have been described, such as acquired 

 manufacturing skill, concentration of population, and the like, 

 then we must make sure of the skill and of the best conditions 

 of existence for the concentrated population. If, in point of fact, 

 shorter hours of labour and taking things easy have contributed 

 to check our rate of progress slightly, there is all the more reason 

 for improving the human agent in industry so as to make work 

 in the shorter hours more efficient. Looking at the stir there 

 now is about technical education and such matters, and the 

 hereditary character of our population, I see no cause to doubt 

 that the future will be even more prosperous than the past. The 

 national life seems as fresh and vigorous as ever. The unrest 

 and complaints of the last few years are not bad signs. But the 

 new conditions must be fully recognized. The utmost energy, 

 mobility, and resource must be applied in every direction if we 

 are only to hold our own. 



REPORTS. 



Fourth Report of the Committee, consisting of Prof. Balfour 

 Stewart (secretary), Profs, Stokes, Schuster, G. Johnstone Stoney, 

 Sir II. E. Roscoe, M.P., Captain Abney, and Mr. G. J. Symons, 

 appointed for the purpose of considering the best methods of 

 recording the Direct Intensity of Solar Radiation. — In their last 

 report the Committee gave a description of a copper inclosure 

 which had been constructed by them. This consisted of a copper 

 cube 3i inches square outside, the faces of which were f of an 

 inch thick. The cube was packed round with felt ^'^ of an inch 

 thick, and the whole was faced outside with thin polished brass 

 plates. Thermometers were inserted into that side of the cube 

 intended ultimately to face the sun, and into the opposite side, 

 by means of which the temperature of these sides could be 



accurately determined. Finally, a thermometer was placed in 

 the vacant space in the very centre of the inclosure. This last 

 thermometer occupies the position that will ultimately be occu- 

 pied by the internal thermometer, upon which the sun s rays are 

 to fall through a hole ; only at this stage the hole had not been 

 constructed. It is obvious that when the instrument is finally in 

 action, with a beam of solar rays (condensed by means of a lens 

 so as to pass through the hole) falling upon the bulb, this ther- 

 mometer will be subject to a heating effect from two separate 

 causes, {a) It will, first of all, be subject to radiation and con- 

 vection from the surrounding inclosure, which is gradually (let 

 us suppose) getting hot through exposure to the sun. {b) It will, 

 secondly, have a beam of solar rays of constant size and of constant 

 intensity (except as to variations arising from atmospheric absorp- 

 tion, seasonal change in the sun's apparent diameter, or change 

 in the sun's intrinsic radiation) continuously thrown upon it through 

 the hole. In fine days when there is no abrupt variation of the 

 sun's intensity the temperature of the internal thermometer will 

 remain sensibly constant, or at least will only vary slowly with the 

 sun's altitude ; and this temperature will be such that the heat lost 

 by radiation and convection from the internal hot thermometer 

 will be equal to the heat which it gains from the sources (a) and 

 [b), save as to a small correction, calculable from the slow 

 variation of the temperature of the thermometer. Now, our object 

 being to estimate accurately the intensity of source {b), we must 

 be able, notwithstanding the gradual heating of the inclosure, 

 to determine how much heat the internal thermometer gains from 

 source (a). That is to say, we must be able to tell what would 

 be the temperature of the internal thermometer if the instrument 

 were still made to face the sun, but without any aperture. For 

 the solid angle subtended by the hole at any point of the bulb is 

 so small that we may regard it as a matter of indiff'erence whether 

 there be a hole or not, except as to the admission or exclusion 

 of direct solar radiation. It was suggested by Prof. Stokes that 

 a simple practical method of doing this would be to expose the 

 instrument, without a hole, to an artificial source of heat, such 

 as a fire or a stove, the intensity of which might likewise be 

 made to vary. By this means the conditions of the instrument 

 when facing the sun might be fairly represented. Experiments 

 of this nature were made at Manchester by Mr. Shepherd, acting 

 under the superintendence of Prof. Stewart, and these were 

 reduced by Prof. Stokes. It was ascertained from these experi- 

 ments that the internal thermometer represented with great 

 exactness the temperature of the cube such as it was 3^ minutes 

 before ; in other words, there was a lagging time of the internal 

 thermometer equal to 3^ minutes. We may thus find what would 

 be the reading of the internal thermometer if the balance were 

 perfect between the gain of heat by direct solar radiation and the 

 loss of heat by communication to the environment ; and as the 

 latter is approximately proportional to the difference of temper- 

 ature of the envelope and internal thermometer, and the 

 deviation from exact proportionality admits of determination by 

 laboratory experiments, we have the means of measuring the 

 former. We must bear in mind that the lagging time of the 

 final thermometer may be different from that of the thermometer 

 with which the experiments were made. It was likewise ascer- 

 tained that the difference between the temperature of the internal 

 thermometer and that of the case need not exceed 20° Fahr., and 

 that a comparatively small lens and hole would suffice for obtaining 

 this result. In consequence of this preliminary information, we 

 have made the following additions to the instrument described in 

 our last report: — (i) We have had it swung like the ordinary 

 actinometers with a motion in altitude and azimuth, and with 

 two moderately delicate adjusting-screws, one for azimuth and 

 another for altitude adjustments. (2) We have had a thermometer 

 centrically placed in the interior. The graduation of the stem 

 is very delicate, and extends from 20° to 120° Fahr., the reading 

 being taken from one of the sides. The bulb is of green flint, 

 and the stem of colourless glass. (3) We have also had a small 

 plate of quartz cut and polished and mounted so as to cover the 

 hole, and to be easily removed and replaced. The object of the 

 plate is to prevent irregularities arising from irregular issue of 

 heated air through the hole, entrance of cooler air blown in by 

 wind, &c., and the choice of material was influenced by the wish 

 to permit of frequent cleaning without risk of alteration by 

 scratching. We ought to mention that as it would be difficult to 

 procure the loan of a good heliostat, and expensive to make, we 

 resolved that in the preliminary experiments the adjustments to 

 keep the sun's image on the hole should be made by the observer. 

 Hence the necessity for the adjusting-screws already described. 



