Dec. 1 6, 1875] 



NA TURE 



133 



can7ing out with models, for the Admiralty, are gradaally accu- 

 mulating the data required on this branch of the subject 



I wish in conclusion to insist again, with the greatest urgency, 

 on the hopeless futility of any attempt to theorise on goodness of 

 form in ships, except under the strong and entirely new light 

 which the doctrine of stream-lines throws on it. 



It is, I repeat, a simple fact that the whole framework of 

 thought by which the search for improved forms is commonly 

 directed, consists of ideas which, if the doctrine of stream-lines 

 is true, are absolutely delusive and misleading. And real im- 

 provements are not seldom attributed to the guidance of those 

 very ideas which I am characterising as delusive, while in reality 

 they are the fruit of painstaking, but incorrectly rationalised, 

 experience. 



I am but insisting on views which the highest mathematicians 

 of the day have established irrefutably ; and my work has been 

 to appreciate and adapt these views when presented to me,* 



No one is more alive than myself to the plausibility of the un- 

 sound views against which I am contending ; but it is for the 

 very reason that they are so plausible that it is necessary to 

 protest against them so earnestly ; and I hope that in protesting 

 thus, I shall not be regarded as dogmatic. 



In truth, it is a protest of scepticism, not of dogmatism ; for 

 I do not profess to direct anyone how to find his way straight to 

 the form of least resistance. For the present we can but feel 

 our way cautiously towards it by careful trials, using only the 

 improved ideas which the stream-line theory supplies, as safe- 

 guards against attributing this or that result to irrelevant or, 

 rather, non-existing causes. 



[To be continued.') 



THE CHANNEL TUNNEL— SUBMARINE 

 EXPLORA TJONS\ 



A N important Report in connection with the proposed 

 -^~*- Channel Tunnel has just been issued by the French 

 Submarine Railway Association, giving the results of a 

 detailed examination of the French coast, and of soundings 

 taken in the bed of the Channel during the past autumn. 

 The subject has on previous occasions been referred to in 

 the pages of this Journal ; % but before giving an account 

 of the recent explorations it may be well briefly to refer to 

 what has already been done. 



A tunnel under the Channel has long been talked of, 

 and many schemes have been brought forward ; but the 

 only one which has been received with general favour is 

 that of Sir J. Hawkshaw, who proposes to carry the 

 tunnel from the South Foreland to near Sangatte. In 

 1864 Mr. E. C. H. Day was employed by Sir J. Hawk- 

 shaw to make a geological survey of the neighbouring 

 coasts with the view of obtaining some guide as to the 

 probable outcrops beneath the Channel ; the map thus 

 produced was published with the early statements of the 

 Company. In 1866 borings were made on both coasts 

 to prove the succession of the strata at points near which 

 the tunnel was to leave the shores ; that on the shore at St. 

 Margaret's Bay traversed 240 feet of upper chalk and 296 

 feet of lower chalk, and was stopped in the gault at a 

 depth of 567 feet from the surface. The boring on the 

 French coast was put down a little north of Sangatte ; it 

 passed through 70 feet of drift- sand, (Sec, 190 feet of chalk 

 with flints, 284 feet of chalk without flints, and was 

 stopped at a depth of 551 feet from the surface owing to 

 an accident to the hole. This boring, therefore, did not 

 reach the Upper Greensand, and the depth to this bed 

 was estimated from information obtained in the deep 

 boring at Calais. This accident was unfortimate, because, 

 owing to a misreading of the accounts of the Calais 



• I cannot pretend to frame a list of the many eminent mathematicians 

 who originated or perfected the stream-line theory ; but I must name, from 

 amongst them, Prof. Rankine, Sir William Thomson, and Prof. Stokes, in 

 order to express my personal indebtedness to them for information and 

 explanations, to which chiefly (however imperfectly utilised) I owe such 

 elementary knowledge of the subject as alone I possess. 



+ Chemin de Fer Sous-Marin entre la France et I'Angleterre. Rapports 

 sur les Bondages executes dans le Pas de Calais en 187s. Fol., Paris, 1875. 



X Vol. i. pp. 160, 303, 63r. Prof. Hubert made a communication to the 

 meeting of the British Association at Bristol, on the folds likely to occur 

 beneath the Channel. (See Nature, vol. xii. p. 407.) 



boring, I believe that the thickness of the lower chalk 

 was considerably over-estimated at Sangatte. 



At a later date soundings were taken along the line of 

 the proposed tunnel, and at varying distances to the 

 south-west of that line ; the instrument used penetrated 

 the bottom for a few inches, and brought up specimens of 

 the ocean floor. The larger number of these were from 

 the superficial covering (sand, &c.), but many brought up 

 pure chalk, and several specimens of gault were obtained 

 near the English coast This examination was not de- 

 tailed enough to test very severely the geological map ; 

 but so far as the information went it tended to confirm 

 the previous surveys ; the only difterence then observed 

 was that the gault appeared to run rather further north 

 towards Dover than would have been expected. But it may 

 be doubtful whether such small borings always give trust- 

 worthy evidence on this point. The lowest beds of chalk 

 are very clayey, and when thoroughly saturated with 

 water are often quite dark and bluish in colour. In fact, 

 these lowest beds, when freshly exposed in railway 

 cuttings, have been at first mistaken for gault by good 

 observers. 



No further e.xplorations have been made till the present 

 year. The concession to the Company was voted by the 

 National Assembly on the 2nd of August, and was signed 

 by Marshal MacMahon on the 5th of the same month. 

 Anticipating the res'ilt of the vote the Company com- 

 menced work in July. By means of a steamer, soundings 

 were taken on the bed of the Channel. A tube was fi.xed 

 at the bottom of the sounding-lead, by means of which 

 specimens were brought up. Various appliances were 

 used, but tubes of from 20 to 22 millimetres in diameter, 

 and 1 5 to 20 centimetres long were found to give the best 

 results. The number of soundings taken per day varied 

 according to circumstances j it averaged 70 or 80, but 

 sometimes reached 100. 



The Commission entrusted with the explorations was 

 presided over by M. Lavalley, and consisted of MM. 

 Delesse, Potier, and Lapparent as geologist, and M. 

 Larousse as hydrographer. The position of the boat was 

 at each observation carefully determined by bearings on 

 landmarks. Every specimen collected was marked and 

 sent to Paris for future determination and reference. In 

 all 1,522 soundings were made ; 753 specimens of the 

 bottom were obtained, of which 335 have been deter- 

 mined with certainty. 



The results show that the outcrop of the gault makes a 

 bend to the north just off the French coast The Com- 

 mission carefidly tested this district by divers (the water 

 being shallow), and they believe that this bend is due to an 

 anticlinal fold of the strata, and not to a fault ; the dip 

 of the beds probably not exceeding 10°. From the French 

 waters across the Channel as far as the obser^'ations went 

 (to within about five miles of the Enghsh coast), the beds 

 run with great regularity. Supposing the observations to 

 be trustworthy, there cannot be a transverse fault of any 

 magnitude along this hne. But the outcrop of the gault 

 lies further to the south than was expected ; in fact, it is 

 striking direct for Folkestone church. As before re- 

 marked, the earlier observations showed the gault near the 

 English shore to run a little further to the north than was 

 expected ; so that here there must either be a roll of the 

 beds or a fault with a downthrow to the south-east.* The 

 engineers point out the importance of following up this 

 inquiry, and doubtless it wUl be done as early as possible 

 next year. 



No one has expected to tunnel through twenty miles of 

 chalk without meeting with a fault, and therefore the possi- 

 bihty of encountering one near the English shore need 

 cause no uneasiness. It may give no extra trouble, or 

 yield no more water than the rest of the work. Faults 

 are often cut in coal workings under the sea, but they do 



* Mr. G. H. Rinahan, writing to me last year, expressed his belief in the 

 existence of a considerable faalt in the Chamiel, wi:b a downthrow to the 



south-east. 



