184 



NATURE 



[Dec. 25, 1879 



Prof. Langley's observations' were chiefly made with 

 the view of shewing that the low estimates of the solar 

 temperature which have recently been made on the basis 

 of Dulong and Petit's formula must be wrong. Prof. 

 Langley compared directly the heat and light received by 

 the sun with that received by the hottest luminous source 

 he could find. He chose the mass of liquid steel obtained 

 in the Bessemer process. The result was that the solar 

 heat radiation was at least eighty-seven times as strong as 

 that of the liquid mass. It is impossible to compare this 

 result directly with the values obtained by Mr. Rossetti ; 

 but a rough idea of a fair agreement maybe obtained. 

 Mr. Rossetti fround the solar radiation to be about forty 

 times as strong as the radiation of a lampblack body in 

 the hottest oxyhydrogen flame he could obtain. Taking 

 account of the emissive power of iron, we find that the 

 radiation of the molten steel must have been a little more 

 than half that of a black body in the oxyhydrogen flame 

 which is possible. Prof. Langley also compared the 

 intensity of light sent out by his two sources, and naturally 

 found a much larger difference. We do not agree with 

 Prof. Langley's remark that the solar light radiation is a 

 more trustworthy indication of the total difference between 

 the sum of all degrees of radiant energy than the heat. 

 In fact the heat radiation is the only correct indication of 

 the total radiant energy. 



Another interesting contribution to the study of radia- 

 tion was lately made by Mr. Nichols. 2 Mr. Nichols 

 heated a platinum wire to successive degrees of incandes- 

 cence by an electric current, and compared the intensity 

 of the luminous radiation in different parts of the spectrum 

 with the incandescence of another platinum wire kept at 

 a constant temperature by means of an electric current. 

 There is a great experimental difficulty in determining the 

 temperatures of the wires, and Mr. Nichols had to content 

 himself with measuring simply their increase in length. 

 Matthiessen's formula will give an approximate idea of the 

 real temperature, but it must be left to future measurements 

 to decide how far Matthiessen's formula can be applied to 

 high temperatures. The chief part of Mr. Nichols' work 

 consists therefore in finding the luminous radiation of 

 platinum, not on an absolute scale, but in terms of an in- 

 candescent platinum wire of fixed but unknown tempera- 

 ture. In order to reduce his measurements to an absolute 

 scale Mr. Nichols compared the radiation of his standard 

 with the luminous radiation of the sun, and then employed 

 Lamansky's measurements of the heating effects of 

 different parts of the solar spectrum. The solar spectrum 

 is however a bad medium of comparison, owing to its 

 discontinuous character. There is, for instance, such a 

 strong atmospheric absorption near D that the radiation 

 of the region near D is seriously weakened ; which 

 weakening is entirely dependent on atmospheric con- 

 ditions, and therefore makes comparisons taken at different 

 times illusory. Thus the final curves obtained by Mr. 

 Nichols for the absolute radiation of platinum wire at 

 different temperatures show a discontinuity near D which 

 is evidently produced by the above-mentioned cause, 

 especially as Mr. Nichols did not use sunlight, but light 

 reflected from clouds. 



Mr. Nichols also tries to deduce from his experiments 

 the fact that platinum a little below its melting point has 

 a much larger absorbing power than at ordinary tempera- 

 tures. The whole argument rests however on the assump- 

 tion that the temperature of a platinum wire is the 

 same as that of a lampblack body when the relative 

 intensity of red and blue light given out by the lampblack 

 body is the same as that given out by the platinum wire. 

 That is to say, Mr. Nichols assumes that the emissive 

 power of platinum is the same for rays of all refrangibi- 

 lities. But it is evident from Mr. N ichols' own measure- 

 ments that the temperature of a petroleum flame (used by 



1 Proceedings of the American Academy. 



" "' Ueber das von gluhendem Platin ausgestrahkc Licht," E. L. Nichols. 

 Gottingen: E. A. Huth.) 



Mr. Nichols) determined in this way is found much too 

 high. It does not require a large correction in this 

 temperature to bring the value of reflective power of 

 platinum at the temperature and by Mr. Nichols to the 

 same value as that found by Provostaye and Dessains for 

 ordinary temperatures. In the memoir of Mr. Rossetti, 

 an idea of which we have tried to give above, this reflecting 

 power of platinum is directly measured at a temperature 

 of the Bunsen flame, and was found to be strikingly in 

 accordance with the number given by Provostaye and 

 Dessains. Arthur Schuster 



NOTE ON A CONSOLIDATED BEACH IN 

 CEYLON 

 A SOMEWHAT interesting consolidated beach exists 

 ■**■ on the west coast of Ceylon, a few miles to the north 

 of Colombo. The writer had only one opportunity of 

 visiting and examining for a short time this formation : 

 but there are certain features in connection with it that 

 cannot fail to be of interest, however short the examina- 

 tion may be. The beach extends continuously in almost 

 a straight line for about four or five miles, and is manifestly 

 in process of formation at thepresent time, as some portions 

 of it are so soft that they can be easily crumbled in pieces 

 by the hand, whilst others are much harder than gneiss, 

 and can only with the greatest difficulty be fractured by 

 means of a heavy hammer. Between these extremes are 

 all gradations of hardness, and the ordinary shells of the 

 coast may be found in almost every part of the beach 

 more or less firmly embedded in the rock. The highest 

 part of the formation is just within reach of the waves at 

 high tide ; but it is difficult to ascertain With any degree 

 of accuracy how far it extends into the sea, on account 

 of the difference between high and low tide being only 

 about two feet. The beach is seen at a glance to be 

 composed chiefly of a faint brownish-coloured rock, with 

 frequent strata of black material of very varied thickness 

 and irregular shape. An examination of specimens shows 

 that the brown rock is composed almost entirely of quartz 

 fragments, and that it possesses only a low specific 

 gravity (291), whilst the darker portions are extremely 

 heavy as well as extremely hard. Several specimens 

 gave a specific gravity of 39, 3'93, 3"94, the dried sand, 

 freed from its carbonate of lime by means of dilute hydro- 

 chloric acid, possessing a specific gravity of 4-32. A 

 microscopic examination of this sand and also of sections 

 of the rock showed that the chief constituent, and that 

 which gave it its dark appearance, was magnetite, 

 corundum in various forms being also present, with here 

 and there a fragment of quartz. One noticeable point 

 was that the fragments of the harder constituents were 

 in nearly every case hardworn, and rounded, whilst the 

 quartz showed traces of recent fracture in the shape of 

 sharp edges and angles. The size of these fragments 

 varies very considerably, those of magnetite ranging from 

 •005 inch to 02 inch, whilst those of quartz are much 

 larger, frequently reaching -04 inch. The corundum frag- 

 ments are intermediate in size and rounded in form. It 

 must be remembered that these specimens were taken 

 from only one part of the formation, near the centre of its 

 length and about the limit of high tide. In other posi- 

 tions the fragments will, no doubt, vary very much, the 

 size depending in a great measure on the power of the 

 current to carry them along the coast and up the beach. 

 It was a matter of regret to the writer that he was not 

 able to inspect carefully both extremities of the reef, and 

 examine fragments from many different portions of it. 

 The cementing material of the beach is carbonate of 

 lime, no doubt from the coral reefs along the coast, as 

 there is no limestone rock in the neighbourhood or along 

 the course of the Kelani River, which debouches to the 

 south of the reef. It is not known whence the magnetite 

 and corundum have been derived, except that they have 



