February 24, 1910] 



NATURE 



489 



an acid solution is likely, not only to live a shorter life, 

 but to suffer sooner and more severely from sulphating and 

 other diseases. E. P. Harrison. 



The Physical Laboratory, Presidency College, 

 Calcutta, February 2. 



The Invention of the Slide Rule. 



Dr. Alexander Russell's remarks on the invention of 

 the slide rule (Nature, January 13, p. 307) are of great 

 interest, particularly his reference to Seth Partridge. 

 There can be no doubt that Partridge deserves much credit 

 for improving the rectilinear slide rule, but I see no escape 

 from the conclusion that the real inventor of the rectilinear 

 slide rule is the one who first made two Gunter's scales 

 to slide together, for purposes of computation. The man 

 who did this is Oughtred. In Mr. Sidney Lee's " Die. 

 of Nat. Biog.," article " Partridge, Seth," and in other 

 publications, the incorrect statement is made that Part- 

 ridge's book, " Description, &c., of. the Double Scale of 

 Proportion," first appeared in print in 1671 or 1672. I 

 have a copy of the book bearing the date 1662. The 

 manuscript was finished: " Saturday night, August first 

 1657." In 1662 Partridge's rules were manufactured, not 

 by "Walter Hayes, but by " Anthony Thompson, living in 

 Hosier-Lane near West Smithfield, in London." 



There is another point of interest. The earliest account 

 of the rectilinear slide rule, printed in Germany, is in 

 Leupold's " Theatrum Arithmetico-Geometricum," Leipzig, 

 1727, p. 71. Leuf^Rld says that he had a manuscript of 

 ten sheets, describing it, but that he did not know the 

 name of the author or the inventor of the instrument. 

 Leupold's description consists of translation, word for 

 word, of extracts from Partridge's book. Thus a historic 

 connection is established between the rectilinear slide rule 

 in England and in Germany. Florian Cajori. 



Colorado Springs, Colorado, February 7. 



Aged Tadpoles. 



The experience of your correspondent Mr. John Don 

 (Februarv 17, p. 458) is no new one. More than twenty 

 years ago we h.ad in a small aquarium in the Charterhouse 

 Museum a tadpole two years of age. To the best of my 

 recollection this veteran never acquired any legs, either 

 hind or front, but the head and body were extraordinarily 

 large. At the present moment I have in my laboratorv 

 seven living tadpoles reared from spawn deposited last 

 spring. Of these, three only have developed hind legs. 

 These appendages appeared rather suddenly in December, a 

 few days after I had supplied, for the first time, some frag- 

 ments of hard-boiled egg. 



The secret of procuring these aged tadpoles is to keep 

 the animals in a vessel with vertical sides, and to afford 

 as little opportunity as possible for them to wriggle into 

 shallow water. I maintain a depth of about 5 inches of 

 water in the aquarium, and find that a subdued light 

 favours the health of the tadpoles. Sexual maturity can 

 hardlv be expected until at least the normal period has 

 elapsed, viz. in the third or even fourth year. 



Oswald H. L.itter. 



Charterhouse, Godalming, February 18. 



Title of the Natural History Museum. 



Ix Nature of February 17 you say (p. 465) : — " No one, 

 50 far as we know, has suggested a suitable and adequate 

 title for the [museum] at South Kensington " (devoted to 

 natural history). This is not a difficult question ; I think 

 " British Museum of Natural History " is both suitable 

 and adequate. Bernard Hobson. 



Tapton Elms, Sheffield, February 18. 



TH'E NEW CANALS OF MARS. 



THE word " new " when applied to a celestial 

 phenotnenon may be used in either of two 

 senses. It may mean new to earthly observation, i.e. 

 one which has never been seen by human beinsrs 

 before, or, secondly, new in itself, that is, one which 

 has had no previous existence. New canals on Mars 

 in the first sense, though always interesting, and at 

 NO. 2104, VOL. 82] 



times highly important, are no novelty at this observa- 

 tory, inasmuch as some four hundred have been 

 discovered here in the last fifteen years. When 

 Schiaparelli left his great work, he had mapped about 

 120 canals; with those detected here since, the number 

 has now risen to between five and si.x hundred. Each 

 of the four hundred thus added to the list, however 

 rich an acquisition at the time it first came to be 

 noticed, was not necessarily otherwise remarkable. 



To observe, however, a canal new in the second 

 meaning of the word, one, that is, that had never 

 existed anteriorly, and to prove the fact, is an astro- 

 nomical detection of far-reaching significance for the 

 bearing it has upon the whole Martian question. 



On September 30, 1909, when the region of the 

 Syrtis Major came round again into view, after its 

 periodic hiding of six weeks due to the unequal rota- 

 tion periods of the earth and Mars, two striking canals 

 were at once evident to the east of the Syrtis in places 

 where no canals had ever previously been seen. Not 

 only was their appearance unprecedented, but the 

 canals themselves were the most conspicuous ones on 

 that part of the disc. They ran one from the bottom 

 of the Syrtis (lat. 20° N., long 285°), the other from 

 a point part way up its eastern side (lat. 17° N., lon.g 

 284°), and, curving slightly to the left as they pro- 

 ceeded south, converged to an oasis, itself new, on 

 the Cocytus (lat. 5° N., long 265°), about two-thirds 

 of the distance to where that canal meets the 

 Amenthes. The Amenthes itself was not visible, ex- 

 cept possibly as a suspicion. With the two main 

 canals were associated several smaller ones, and at 

 least two oases which had never been seen before, 

 and from the interconnection of all of them these 

 clearly made part of the new piece of Martian triangu- 

 lation. 



The phenomena were recorded in many independent 

 drawings by Mr. E. C. Slipher and the director, and 

 in the course of the next few days were photographed, 

 appearing on the plates to the eye as the most con- 

 spicuous canals in the presentment of the planet. It 

 is opportune that detailed photography of Mars in 

 Mr. Lampland's skilful hands should have been so 

 perfected as to make this possible ; for the photo- 

 graphs taken by both Mr. E. C. Slipher and the 

 director record these canals so that anyone may see 

 them. There are thirty images, more or less, on ea-ch 

 plate, and the canals appear on every image ; on 

 some more distinctly than on others, owing to the 

 state of our air at the time, but recognisably on all; 

 for each image had a pose of about two seconds and 

 a half, and its definition varied according to the seeing 

 at the time. Owing to the grain of the plate being 

 much coarser than that of the eye, the two canals 

 appear merged in one in the photographic images as 

 a single line, its linear character, however, being quite 

 distinct to one of good eyesight. 



The photographs of this region taken in 1907 show 

 no such feature. 



No remembrance of ever having seen them before 

 could be recalled by either observer, both being 

 familiar with the planet, except that Mr. Slipher 

 turned out to have drawn one of them the evening 

 previous. 



The record books were then examined, when it 

 appeared that not a trace of them was to be found in 

 the drawings of August, July, June, or May when 

 this part of the planet was depicted. That they had 

 not been observed in previous years was then con- 

 clusively ascertained by examination of the records of 

 those years. The record of canals seen here is 

 registered after each opposition in a fresh map of 

 the planet's surface. This has been done since the 

 beginning of the critical study of Mars at this observa- 



