^rarcll lo. 1887] 



NATURE 



437 



OUR BOOK SHELF 



The Deviatiim of the Compass in Iron Ships considered 

 Pracliailly. liy VV. H. Rosser. Second Edition, 

 with considerable additions. (London : James Imray 

 and Son, 18S7.) 



Rememherixi; the number of booivs already published 

 treating in a practical form of compasses, their deviations 

 on board iron ships, and the consequent adjustments, 

 some persons may be disposed to ask, " What purpose will 

 be served by an addition to them?'' In answer it 

 may be said that this, the second edition of a use- 

 ful work by an author who bases his knowledge on the 

 teaching of the " Admiralty Manual," and knows from 

 instructing others their many difficulties, can hardly fail 

 to be welcome to those having neither time nor ability to 

 assimilate the subject without a guide at every turn. 



Whilst we hope that Mr. Rosser's later edition will be 

 duly appreciated, there is a certain definition which, for 

 the sake of simplicity and accuracy, we would fain Eee 

 removed from it. At pp. 30 and 31, clear definitions 

 are given of true, magnetic, and compass courses 

 Why not let well alone, and not complicate the 

 matter by introducing the term "correct" magnetic 

 course ? .A reference to the later editions of the Admiralty 

 publications on the deviation of the compass shows that 

 the word " correct '' in connection with " magnetic 

 course' has been entirely omitted, apparently as no 

 longer serving any purpose. 



The concluding paragraph of the preface on patent 

 compasses is hardly fair to Sir William Thomson's. The 

 principles involved in the construction of his compass are 

 not in themselves novelties, but he has done world-wide 

 good by showing in it how that enemy of compasses — 

 friction -may be avoided, whilst at the same time he has 

 produced a card which is almost free from oscillation 

 when the ship rolls heavily. 



Travels in the Wilds of Ecuador. By Alfred Simson. 

 (London : Sampson Low, 1886.) 



" No one with the spirit of roaming within him," says the 

 author of this book, '• can live long in Ecuador without 

 cherishing a growing desire to explore its unknown parts." 

 Some time ago, accordingly (the exact date is not men- 

 tioned), he started with a companion from Guayaquil for 

 Banos, and from Banos they went through the forest to 

 the village of .Aguano, on the River Napo, completing the 

 road in eighteen days' actual walking, or forty-five days' 

 foot journey, including necessar)' stoppages. At Aguano 

 they were obliged to remain forty-two days, which they 

 spent partly in collecting Lepidoptera, partly in making 

 voyages of discovery by land and water in search of pro- 

 visions. They then made their way in canoes down the 

 Napo to the .Amazon, which they reached after a voyage 

 of twenty-five days. .At Iquitos the two friends parted, 

 Mr. Simson's companion setting out to explore the L'ca- 

 yali, while Mr. Simson himself joined a Mr. Reyes in an 

 expedition up the River Putumayo. 



The story is very simply and pleasantly told, and those 

 who like to read about distant lands of which little is 

 generally known, will find much to interest them in the 

 author's record of his adventures. The best parts of the 

 book are those in which he describes the Indian tribes of 

 Ecuador, whose habits and modes of thought and feeling 

 he closely observed. He also notes some rather curious 

 facts in natural history. Probably few persons have ever 

 heard of " the roaring of an alligator." " I heard it 

 myself," says Mr. Simson, "on one occasion in the case 

 of a huge beast who appeared to be following a female 

 of his species." The animal was swimming very rapidly, 

 diving and rebounding up to the surface of the water. 

 Mr. Simson was in a small Rob Roy canoe, and remained 

 still to watch his manoeuvres. Immediately the alligator 

 saw the canoe, he "came towards it, roaring like a bull at 



each bound above water." .As he was diving, Mr. Simson 

 (who was unarmed) forced the canoe straight over him, 

 and so escaped. " Curiously enough," we are told, "not 

 half an hour after this episode, an alligator jumped from 

 a steep bank over my canoe, and only just cleared it, 

 as I was distractedly paddling along under the shore, 

 and inadvertently startled the reptile above me." 



LETTERS TO THE EDITOR 



[Th{ Editor Jots not hold himself responsibU for opiniom tx- 

 pressed by his correspondents. Neither can he undertake to 

 return, or to correspond with the writers of, rejected manu- 

 scripts. No notice is taken of anonymous communications. 



[ The Editor urgently requests correspondents to keep their letters 

 as short as possible. The pressure on his space is so great 

 that it is impossible otherwise to insure the appearance even 

 of communications containing interesting and novel facts. ] 



Tabasheer 



As I have occasionally found the curious stony plug of which 

 Mr. Thiselton Dyer writes (N.\TURE, vol. xxxv. p. 396), in the 

 joints of bamboos accidentally broken, and been much exercised 

 as to the nature and origin of the phenomenon, I have been 

 much interested by his paper. May I further suggest that it is 

 to a certain extent palhological — due, that is, to arrested 

 gro-,vth, either longitudinal or lateral, in the shoot next above 

 the joint in which the stony secretion or sediment is found. 



In the onrush of tropical growth in the young shoot, Nature, 

 after flooring the knot, has poured in, as it were, sap and silica 

 sufficient for a normal length and width of stem to the knot 

 next above it. But by some check to the impulse, or irregularity 

 of conditions, the portion of stem thus pro%ided for is shorter or 

 narrower than intended ; and the unused silica is left behind as 

 a sediment, compacted by the drying residuum of sap. It is a 

 question only to be settled by close examination of a great 

 number of examples. 



Something like it occurs, however, in the case of our own 

 wheat. Larger joints, that is, and stronger walls are commonly 

 found where the length of stem between joint and joint is a 

 short one. As in the bath for electroplating the same amount of 

 silver is deposited in a given time on a single penny as on a tea 

 service of many pieces, so in the case of quick-growing siUcated 

 stems it would seem as if the same average amount of material 

 were provided by the mounting sap, and the constructive use 

 actually made of it determined by many accidents. In the 

 wheat stem the silica is difi'erenily placed ; in the fiercely- 

 growing bamboo shoot the mineral in excess is left behind in a 

 crude form, and disregarded. That is what I should expect to 

 find. Henry Cecil 



Bregner, Bournemouth, March I 



Temperature and Pressure in Jamaica 

 The following table of elevations and averages is not as 

 perfect as might be wished, but as some years mut pass before 

 it can be greatly improved, it is here given as one of many 

 results obtained by the Meteorological Service in Jamaica : — 



Station ^tion ^'^''^"^^ M=^x. Mean Min. Range 



Feet Inches a a > a 



Kingston o 30-00 87"o 78'2 710 i6'0 



Kempshot 1773 28-20 80-5 72-7 680 12-5 



Cinchona Plantation ... 4907 25-27 68-5 62-6 57-5 il-o 



Portland Gap 5477 24-71 69-0 59-7 54-6 14-4 



Blue Mountain Peak... 7423 2314 71-1 557 46-3 24-8 



In Nature, vol. viii. p. 200, it was suggested that the fall of 

 temperature, 5 7" was connected with the fall of pressure 5.^ by 

 the equation 



5 7'= \.5P, 

 where h was taken equal to 3'-23. 



We can now correct this expression and take 

 lT-\.iP+ii (hP)-, 

 where \ = 2°-92, and .u — o'-o8. But these values relate to 

 mean temperatures ; for minimum temperatures K = o°'^(>, and 

 M = 0^-40. 



These expressions and their connection are important, and it 



