Nov. 21, 1878] 



NATURE 



53 



you will in fairness allow me to take advantage, to prove 

 that your article does scant justice to Mr, Steams' predecessors 

 in the application of the duplex system to long submarine 

 cables, and that their success has been something more than 

 " only partial " in the opinion of those who have employed their 

 system. 



Mr. Steams' first success on a long cable dates from a 

 few days ago. In Febraary, 1876, Dr. Muirhead and myself 

 obtained experimentally a perfect balance on the Suez-Aden 

 cable, which, though shorter in miles, is electrically longer than 

 either of the Anglo Company's cables from Yalentia on which 

 Mr. Steams has worked. 



In March of the same year Mr. J. Muirhead and myself 

 duplexed the Marseilles-MaJta cable, which, though only 825 

 miles in length, is worked by Sir W. Thomson's syphon recorder, 

 and our system has been in commercial operation on the line 

 ever since. 



Early in 1877 Dr. Muirhead applied the system to the Aden- 

 Bombay Cable, which is longer in miles and far longer electrr- 

 cally than either of the cables from Valentia, and since that time 

 this line, as well as that from Suez to Aden, has been worked 

 "duplex" whenever the traffic required it, to the entire satisfac- 

 tion of the company. 



Next, as to your remark that " Mr. Muirhead has been at work 

 duplexing the Direct United States Cable with some prospect of 

 success," the facts of the case are these : — 



The cable, in its linear measurement, exceeds the longest 

 Valentia cable by 543 miles ; electrically it is twice as long. 



It is worked with the mirror galvanometer, and not with the 

 recorder, and these circimistances render the difficulty of obtain- 

 ing a duplex balance upon it immensely greater than upon any 

 of the other lines referred to. 



Notwithstanding the difficulties mentioned. Dr. Muirhead and 

 myself, in April last, obtained a perfectly satisfactory balance, 

 enabling us to transmit sixteen words a minute in both direc- 

 tions at the same time, between Ireland and Nova Scotia, 

 a cable distance of 2,420 nautical miles. Herbert Taylor 



7, Pope's Head Alley, Lombard Street 



P.S. — Since writing the above my attention has been called 

 to Nature, vol. xv. p. 180, containing an article on this subject, 

 in which the applications of Muirhead's system to some of the 

 cables referred to in my letter are spoken of as being the first 

 practical successes in submarine duplex telegraphy. 



Remarkable Colour- Variation in Lizards 



Mr. Wallace's observations in Nature, vol. xix. p. 4, 

 on a black variety of the common lizard of Capri, as met with 

 on the neighbouring islet of Faraglioni, induces me to refer to a 

 similar appearance in the lizards frequenting the islet of Filfla, 

 on the southern coast of Malta. As recorded in my book, 

 " Notes of a Naturalist in the Nile Valley and Malta," p. 80, I 

 have stated that diu-ing a visit to Filfla I was surprised to find 

 that all the lizards on the rock were a beautiful bronze black and 

 so much tamer than their timider brethren on the mainland. 

 Many individuals were so tame that they scrambled about our 

 feet and fed on the refuse of our luncheon. I subsequently sent 

 specimens of this variety, or rather race, to Dr. Giinther, 

 j F.R.S., who pronounced them identical with the Podarcis muralis, 

 so extremely plentiful in Malta and Gozo. Now although the 

 denizens of the two latter islands present divers shades of colour- 

 ing, I never observed (and I looked carefully during several years) 

 a black or dark-coloured individual. Filfla is about 600 yards in 

 circumference and three miles distant from Malta. It is formed 

 of the upper miocene limestone, and marks an important fault 

 or down-throw which runs along the coast of Malta opposite, 

 by which, as seen in the sketches Figs. I and 2 of the work re- 

 ferred to, it appears clear that the severance took place long subse. 

 quent to the days of the pigmy elephants, hippos, giant dormice 

 and tortoises, whose remains have been found in such abimdance 

 in the crevices of the rocks -opposite Filfla. There is no 

 verdure on this bare rock-islet, the surface of which is dark- 

 coloured, whilst its crevices shelter the lizards and furnish abodes 

 for the nests of Manx and cenereous shearwaters, whose docility 

 at the breeding season is equally remarkable, both reptile and 

 ; birds being like their compeers of Enoch Arden's island, "so 

 I wild that they were tame." 



I Probably the dark colouring is protective, and thus consorting 

 well with the surrounding surfaces, would tend to preserve them 



from the harriers, buzzards, and hawks which tarry in the 

 Maltese Islands during the spring and autumn migrations 

 November 11 A. Leith Adams 



The remarkable case of local colour- variation in lizards com- 

 municated by Mr. A. R. Wallace to Nature (vol. xLx. p. 4), 

 had already been investigated by Dr. Theodor Eimer, an abstract 

 or translation of whose memoir on the subject, entitled " Lacerta 

 muralis csmlea, a Contribution to the Darwinian Theory," is 

 to be found in Ann. and Mag. Nat. Hist., 1875, 4th ser., vol. 

 xvi. p. 234. J. Wood-Mason 



54, Claverton Street, S.W., November 16 



The Drought 



At the present time, when more attention is paid to the influ- 

 ence of meteorological phenomena upon society, it would be 

 useful to give some information as to the bearing of the local 

 droughts and famines on our trade and the prospect of its revival. 

 The China and Indian trades have not yet recovered. The 

 droughts have also affected Egypt and Morocco. In the West 

 Indies, Guiana, Venezuela, Colombia, and Brazil they are still 

 operative. 



They act to prevent the growth of produce, and in many 

 countries, by reducing the water-ways, they impede its ship- 

 ment. The people cannot consume our imports, the transit of 

 which is in some cases impeded. The whole of these difficulties 

 affects the exchanges and interferes with the money market and 

 remittances. 



The severity of the crisis is abating, but we can hardly feel 

 assured of the revival of trade in Europe and the United States 

 till there is a complete recovery over the vast areas of producing 

 and consuming countries. 



Thus the study of meteorological phenomena and facts acquires 

 a new value for practical men and society at large, as stated by 

 Prof. Jevons in your last number, Hyde Clarke 



Sewerage and Drainage 



In Nature, vol, xix. p, i, you touch upon a most important 

 point in sanitary engineering which I have for ten years been 

 striving by every means in my power to press upon the public, 

 and I therefore venture to trouble you with a few lines on the 

 subject. 



The most important argument in favour of the exclusion of 



storm water from sewers consists, as you say, in the liability of 



road detritus to form deposits on the wide flat surface of any 



! channels large enough to convey to one point an exceptionally 



j heavy fall of rain over the area covered by a town, and the in- 



[ evitably slow course of the infinitely smaller volume of sewage 



; flowing or stagnating in dry weather along the same channels. 



j When separate sewers are provided for sewage they can be 



made of such smaller capacity as to keep up a constant flow 



i from the houses in which the sewage is produced, to the land 



\ upon which it is to be purified, because the volume of liquid 



! will very nearly correspond with the water supply, and the 



'' engineer has safe data upon which to adjust his means to the 



I desired end. 



i In every town there are, or were, lines of natural watercourses, 

 '■ and if the scavengers' work is properly done the rain-water from 

 i roofs and streets may safely be discharged into any of these by 

 short lengths of drains, less liable to be encumbered with de- 

 posits of road detritus, and with the certainty that if such ac- 

 \ cumulations should occur, they will be perfectly harmless firom 

 the absence of sewage. 



The experiments of Mr. Way with London street water have 

 been seized upon by Mr. Baldwin Latham in order to cover his 

 retreat from the false position unfortunately taken up by himself 

 and most of our senior engineers in the earlier days of sanitary 

 science, and as he knows as well as any one eke that it was a 

 grand mistake to confuse and combine sewerage and drainage in 

 one system, I agree with you in thinking it a pity that he has not 

 acknowledged the facts more distinctly in the recent edition of 

 his well-known work. 



The greater proportion of the impurities detected by ProL 

 Way in the few samples of London street water which he tested 

 are mineral ones which would be comparatively harmless, and, in 

 the opinion of Dr. Voelcker, the experiments must have been 

 vitiated by some mistake. Now as the latter authority has 



