Dec. i8, 1873J 



NATURE 



135 



"May we not from these ideas be justified in defining a 

 metal, provisionally, as a substance the absorption spectrum of 

 which is generally the same as the radiation spectrum, while the 

 metalloids are substances the absorption spectrum of which, 

 generally, is not the same ? 



" In other words, in passing from a hot to a comparatively 

 cold state, the plasticity of these latter comes into play, and we 

 get a new molecular arrangement. Hence are we not justified 

 in asking whether the change from i/xygen to ozone is but a type 

 of what takes place in all metalloids ? " 



Abstract of paper " On the Quantitative Analysis of certain 

 Alloys by means of the Spectroscope," by J. Norman Lockyer, 

 F.R.S., and William Chandler Roberts, Chemist of the Mint. 



The authors, after referring to experiments which showed 

 clearly that the spectroscope might be employed to detect mi- 

 nute differences in the composition of certain alloys, proceed to 

 give an account of the researches which they had instituted with 

 a view to ascertain the degree of accuracy of which the method 

 is capable. 



The image of an electric-spark passing between the un- 

 known alloy and a fixed electrode being thrown by means of a 

 lens on the slit of the spectroscope, the phenomena observed 

 were found to vary with the coniposiiion of the alloys ; and 

 further, by arranging them together with known check-pieces on 

 a suitable stand, and bringing them in turn under the fixed elec- 

 trode, the composition of the unknown alloys was determined 

 by comparison with the known check-pieces. 



The shape of the electrode ultimately adopted was stated ; the 

 ]jieces were held in their places by suitable metallic clips. Special 

 attention was then directed to the adjustment of the length of the 

 spark, which was found to materially influence the phenomena. 

 The method adopted consisted in placing the variable electrode 

 in the field of a fixed microscope having a 3- or 4-inch objective, 

 and adjusting the summit of this electrode to coincide with the 

 spider lines of the eye-piece. 



After a series of experiments on alloys of zinc and cadmium 

 of various compositions, the results of which were shown on a 

 curve, more extended trials were made with the gold-copper 

 alloy employed in coinage, which was peculiarly suited to these 

 researches in consequence of the known method of assay having 

 been brought to so high a state of perfection (the composition 

 being determined with accuracy to the tti^uu P^rt of the original 

 assay-piece of about 7 grains), and from the fact that reliance 

 can be placed on its homogeneity. The paper is accompanied by 

 a series of four curves, which show the results of experiments, 

 and in which the coordinates are given by the ordinary method 

 of assay, and by the spectroscopic readings. 



The chief practical advantage which appeared to flow from 

 this inquiry was that, if it were possible to replace the parting 

 assay by the spectroscopical method, a great saving of time in 

 ascertaining the value of gold bullion would be effected. 



Institution of Civil Engineers, Dec. 9. — T. Hawksley, 

 president, in the chair. — " On the Geological Conditions affect- 

 ing the Constructing of a Tunnel between England and France, " 

 by Mr. Joseph I'restwich, F.K.S. The author reviewed the 

 geological conditions of all the strata between Harwich and 

 Hastings on one side of the Channel, and between Ostend and 

 St. Valery on the other side, with a view to serve as data for any 

 future projects of tunnelling, and to show in what directions in- 

 quiries should be made. The points considered were the litho- 

 logical characters, dimensions, range and probable depth of the 

 several formations. The London clay, at the mouth of the 

 Thames, was from 200 feet to 400 feet thick, while under 

 Calais it was only 10 feet, at Dunkirk it exceeded 264 feet, and 

 at Ostend it was 44S feet thick. He considered that a trough 

 of London clay from 300 feet to 400 feet, or more, in thickness 

 extended from the coast of Essex to the coast of France, and, 

 judging from the experience gained in the Tower Subway, and 

 the known impermeability and homogeneity of this formation, 

 he saw no difficulty, from a merely geological point of vieM", 

 in the construction of a tunnel, but for the extreme distance 

 — the nearest suitable points being So miles apart. The lower 

 Tertiary strata were too unimportant and too permeable for 

 tunnel work. The chalk in this area was from 400 feet to 1,000 

 feet thick ; the upper beds were soft and permeable, but the 

 lower beds were so argillaceous and compact as to be com- 

 paratively impermeable. In fact, in the Hainaut coal fields 

 they effectually shut out the water of the water-bearing tertiary 

 strata from the underlying coal measures. Still, the author did 



not consider even the lower chalk suited for tunnel work, owing 

 to its liabilty to fissures, imperfect impenneability, and exposure 

 in the Channel. The gault was homogeneous and impermeable, 

 but near Folkstone it was only 130 ft. thick reduced to 40 ft. at 

 Wissant, so that a tunnel would hardly be feasible. The Lower 

 Greensands, 260 ft thick at Sandgate, thinned off to 50 ft. or 

 60 ft. at Wissant, and were all far too permeable for any tunnel 

 work. Again, the Wealden strata, 1,200 ft. thick in Kent, 

 were reduced to a few unimportant rubbly beds in the Boulon- 

 nais. To the Portland beds the same objections existed as to 

 the Lower Greensands. both were water-bearing strata. The 

 Kimmeridge clay was 360 ft. thick near Boulogne, and no doubt 

 passed under the Channel, but in Kent it was covered by so 

 great a thickness of Wealden strata as to be almost inaccessible ; 

 at the same time it contained subordinate water-bearing beds. 

 Still, the author was of opinion that, in case of the not improb- 

 able denudation of the Portland beds, it might be questionable 

 to carry a tunnel in by the Kimmeridge clay on the French coast, 

 and out by the Wealden beds on the English coast. The oolitic 

 series presented conditions still less favourable, and the lower 

 beds had been found to be water-bearing in a deep artesian 

 well recently sunk near Boulogne. The experimental deep- 

 boring now in progress near Battle would throw much light on 

 this part of the question. The author then passed on to the 

 consideration of the Palaeozoic series, to which his attention 

 was more particularly directed while making investigations, as 

 a member of the Royal Coal Commission, on the probable 

 range of the coal measures under the south-east of England. 

 He showed that these rocks, which consisted of hard 

 Silurian slates, Devonian and carboniferous limestone and 

 coal measures, together 12,000 ft. to 15,000 it. thick, passed 

 under the chalk in the North of France, outcropped in the Bou- 

 lonnais, were again lost under newer formations near to the 

 coast, and did not reappear until the neighbourhood of Frome 

 and WcUs was reached. But, although not exposed on the sur- 

 face, they had been encountered at a depth of 1,032 ft. at Calais, 

 985 ft. at Ostend, 1,026 ft. at Harwich, and 1,114 ft. in London. 

 They thus seemed to form a subterranean table land of old rocks, 

 covered immediately by the chalk and Tertiary strata. It was 

 only as the southern flank of this old ridge that the Jurassic and 

 Wealden series set in, and beneath these the Palaeozoic rocks 

 rapidly descended to great depths. Near Boulogne these strata 

 were already 1,000 ft. thick ; and at Hythe the author estimated 

 their thickness might be that or more. Supposing the strike of 

 the coal measures and the other Palteozoic rocks to be prolonged 

 from their exposed area in the Boulonnais across the Channel, 

 they would pass under the Cretaceous strata somewhere in the 

 neighbourhood of Folkestone, at a depth estimated by the author 

 at about 300 ft. , and near Dover at about 600 ft, , or nearly at the 

 depth at which they had been found under the chalk at Guines, 

 near Calais, where they were 665 ft. deep. These Paleozoic 

 strata were tilted at high angles, and on the original elevated 

 area they were covered by horizontal Cretaceous strata, the base- 

 ment beds of which had filled up the interstices of the older rocks 

 as though with a liquid grouting. The overlying mass of gault 

 and lower chalk also formed a barrier to the passage of water 

 30 effectual, that the coal measures were worked without diffi- 

 culty under the very permeal^le Tertiary and upper chalk of the 

 North of France ; and in the neighbourhood of Mons, notwith. 

 standing a thickness of from 500 ft. to 900 ft. of strata charged 

 with water, the lower chalk shut the water out so effectually 

 that the coal measures were worked in perfect safety, and were 

 found to be perfectly dry under 1,200 ft. of these strata combined. 

 No part of the Straits exceeded i85 ft. in depth. The author, 

 therefore, considered that it would be perfectly practicable, so far 

 as safety from the inflirx of the sea water was concerned, to drive 

 a tunnel through the Palaeozoic rocks under the Channel between 

 Blanc Nez and Dover, and he stated that galleries had actually 

 been carried in coal, under less favourable circumstances, for two 

 miles under the sea near Whitehaven. But while in the case of 

 the London clay the distance seemed almost an insurmountable 

 bar, here again the depth oflered a formidable difficulty. As a 

 collateral object to be attained, the author pointed to the great 

 problem of the range of the coal measures from the nv.ighbour- 

 hood of Calais in the direction of East Kent, which a tunnel in 

 the Pal.ieozoic strata would help to solve. These were, accord- 

 ing to the author, the main conditions which bore on the con- 

 struction of a submarine tunnel between England and France. 

 He was satisfied that on geological grounds alone, it was in one 

 case perfectly practicable, and in one or two others it was possibly 

 so ; but there were other considerations besides those of a geolo- 



