Peb. 8, 1877] 



NATURE 



321 



importance to this as a source of the materials in our deep 

 deposits. 



2. We have the dust of deserts, which is carried great dis- 

 tances by the winds, and which, falling upon the ocean, sinks to 

 the bottom and adds to the depositions taking place. In the 

 trade-wind regions of the North Atlantic we have a very red- 

 coloured clay, in deep water, which is largely made up of dust 

 from the Sahara. Such dust frequently falls in this region as what 

 is called blood- rain. 



3. We have the loose volcanic materials, which have been 

 shown to be universally distributed as floating pumice, or as 

 ashes carried by the wind. 



This short review shows that the clay in shore deposits is 

 chiefly derived from river and coast detritus. As we pass beyond 

 about one hundred and fifty miles from the shores of a continent 

 the character of the clayey matter changes. It loses its usual 

 blue colour, and becomes reddish or brown, and particles of 

 mica and rounded pieces of quartz give place to pumice, crystals 

 of sanidin, augite, olivine, &c. All this goes, I think, to show 

 that in deposits far from land the clay is chiefly derived from 

 volcanic debris, though in the region of the North Atlantic trade- 

 winds much of it may be derived from the feldspar in the dust 

 of the Sahara. 



The pumice which floats about on the surface of the sea must 

 be continually weathering, and the clay which results and the 

 crystals which it contains will fall to the bottom, mingling with 

 the deposit which is in course of formation. In our purest glo- 

 bigerina ooze this clay and these crystals are present. If a few 

 of the shells, say thirty foraminifera, are taken from such a 

 deposit, and carefully washed, and then dissolved away with 

 weak acid, a residue remains, which is red -brown or grey in 

 colour, according to the region from which the ooze came. If 

 the same number of shells be collected from the surface and dis- 

 solved away in the same manner, no perceptible residue is 

 observed. The clayey matter would therefore seem to have 

 infiltrated into the shells soon after they fell to the bottom. 



I have already mentioned several instances of pumice-stones 

 having been found on coral-reefs. Many more instances could 

 be given. These stones, undergoing disintegration in these 

 positions, add clay, crystals of augite, hornblende, magnetic 

 iron ore, &c., to the limestones which the coral animals are 

 building up. 



I have found these crystals in the limestones and red earth of 

 Bermuda, and in a specimen of the limestone from Jamaica. 



This observation, it appears to me, points out that the red 

 eai th of Bermuda, Bahamas, Jamaica, and some other limestones, 

 may originally have been largely derived from fragmental volcanic 

 materials, which were carried to the limestone while yet in the 

 course of formation. There are also small particles of the per- 

 oxide of manganese in the red earth of Bermuda. 

 ^To be continued.) 



CHEMISTRY AND TELEGRAPHY^ 



T^ISCLAIMING at the outset any pretensions which could 

 ^^ be advanced in his behalf for the honour conferred upon 

 him. Prof. Abel assumed that his advancement to the position of 

 president was intended more as a recognition of the .special im- 

 portance of chemical science in its application to telegraphy. 

 Proceeding upon this assumption he made chemical science the 

 basis of his address, and went on to show the principal direc- 

 tions in which it bears importantly upon the work of the tele- 

 graph engineer. 



No stronger evidence of the value attaching to a combination 

 of chemical with electrical research need be sought for than that 

 which is to be found in the labours of the late Dr. Matthiessen. 

 His investigations into the causes of the differences in the resist- 

 ance of various kinds of commercial copper were followed by 

 most important results. 



The series of experiments so carefully conducted by him 

 showed the influence which the principal metalloids and metals 

 ""mown to be naturally associated \vith copper exerted upon the 

 ponducting power of the pure metal, and he afterwards deter- 

 lined the conducting power of important varieties of commercial 

 Dpper, and thus rendered it possible to assign to their real causes 

 le enormous differences in the value of various kinds of commer- 

 cial copper as conductors of electricity. For instance, amongst the 

 many facts established by Matthiessen's experiments was the im- 



I Abstract of Address at the opening meeting of the Society of Telegraph 

 Engineers, January 24, by the President, Prof. Abel, F.R.S. 



portant one that by no combination of any other metal or alloy 

 was it possible to increase the conducting power of pure copper, 

 but that, on the contrary, a most prejudicial effect was exerted 

 upon it by the presence of some of the non-metallic elements — 

 notably oxygen and arsenic — which are almost invariably to be 

 found as impurities in the copper of commerce. It was these 

 non-metallic impurities he found rather than the presence of any 

 of the other metals which chiefly impaired the conductivity of 

 copper, although both iron and tin exercised a deleterious influ- 

 ence. Thus, fixing the conductivity of pure galvano-plastic cop- 

 per at 100, the addition of merely traces of arsenic reduced it to 

 60 ; while an addition of 5 per cent, brought it as low as 6"5 ; 

 the existence, again, of i'3 per cent, of tin in pure copper 

 reduced its conductivity to 50 4, and with only o'48 per cent, of 

 iron present the conductivity fell to 36. 



Specially interesting were the experiments made by Mat- 

 thiessen to ascertain the cause of the good effects which had long 

 before his day been observed to be produced upon the working 

 qualities of refined copper by the addition of minute quantities 

 of lead. The existence of 0*25 per cent, of lead in copper 

 renders it so rotten that it cannot be drawn into wire ; the pre- 

 sence of even so minute a trace as 0"l per cent, unfits it for wire- 

 drawing. Some special action must therefore take place during 

 the melting of copper which would serve to account for the 

 toughening and softening effects obtained by the addition of a 

 small quantity of lead. The fact that the copper when sub- 

 jected afterwards to a most careful analysis shows nothing but 

 the merest traces of lead, would indicate that during the process 

 of melting, the lead combines with and removes from the copper 

 some impurity which would otherwise materially affect its 

 toughness and ductility. The well-known affinity of lead for 

 oxygen, combined with the fact that the presence of oxygen 

 in copper beyond some narrow limit was known to affect its 

 quality prejudicially, afforded good reasons for supposing that 

 this impurity could be nothing else than oxygen, and this view, 

 which was further supported by the beneficial influence of lead 

 when employed in casting operations with copper and gun metal, 

 received the strongest confirmation of its correctness from 

 Matthiessen's experiments. Thus, the addition of o*i per cent, 

 of lead to a sample of copper (the two being fused together in a 

 current of carbonic acid), raised its conductivity from 87'25 to 

 93, and the amount of lead remaining in the metal after that was 

 too minute to be detected. So with tin, the alloying of i'3 per 

 cent, of which with copper reduced, as has been already stated, its 

 conductivity to 50*4 ; yet on melting the sample fused in contact 

 with air with o'l percent, of tin raised its conductivity to 94 '5 5. 

 It was these investigations of Matthiessen which indicated to 

 the wire manufacturer whence he could obtain or hov/ best fulfil 

 the conditions for the purity of a quality of copper, which would 

 meet the requirements of a conductor whose size might be laid 

 down by the telegraph engineer, whilst his researches into the 

 preparation of alloys brought the most valuable aid to the B.A. 

 Committee of 1 861, in their determination of the standards of 

 electrical resistance. 



But it is not only in facilitating the selection of suitable 

 materials for conductors, as well as in raising their quality as such 

 that chemical science has brought important aid to the telegraph 

 engineer ; it has been most usefully applied in the investigation 

 and determination of the materials most suitable as the dielectrics 

 of telegraph cables, and it is in this direction that telegraphy may 

 look in the future for the m.ost valuable results from the labours 

 of the chemist. Dr. Miller's investigations (instituted at the 

 desire of the Submarine Telegraph Committee) into the causes 

 of the decay of gutta-percha and india-rubber, confirmed the re- 

 sults which Hoffman had already communicated in i860 to the 

 Chemical Society and which Mr. Spiller had obtained some years 

 afterwards. But Miller examines more in detail than either of 

 his predecessors has done, into the changes which these gums 

 undergo, and firmly established the fact that the alterations in 

 their structure, resulting in the gradual destruction of their insu- 

 lating powers, was due entirely to atmospheric influence, acceler- 

 ated by the exposure of the material to hght. He further pointed 

 out that intermittent exposure to moisture, especially if solar light 

 has access, rapidly destroys gutta-percha, whilst if kept continu- 

 ally immersed in water it remains unchanged for an indefinite 

 period. He also showed that commercial gutta-percha contained, 

 previous to any special exposure to oxidising influences, as much 

 as 15 per cent, of resinous matter and a considerable amount of 

 water (2*5 per cent.) mechanically diffused through it. Con- 

 siderable improvements had doubtless been made since that date 

 in the mechanical processes for preparing gutta-percha, but these 



