Dec. 30, 1880] 



NA TURE 



19- 



shows the various causes in operation at the time to 

 instigate such voyages, causes mainly poHtical and 

 commercial. Other influences were however at work, 

 not the least of which was "the total transformation 

 which astronomy and geography had undergone " during 

 the sixteenth century. The narratives here given are 

 those of Hawkins's arid Frobisher's three voyages, Drake' s 

 voyages of 1577 and 15S5, Gilbert's voyage of 1583, 

 Amadas and Barlow's voyage, 1584 ; Cavendish's first and 

 last voyages, and Raleigh's voyage to Cluiana. Prefixed 

 to eacli narrative is a short historical introduction. 



LETTERS TO THE EDITOR 



[The Editor doc-s not hold himself responsible for opinions expressed 

 by his eorrespondtnts. Neither can he undertake to return, or 

 to correspo/id with the writers of, rejected manuscripts. No 

 notice is taken of anonymous communications. 

 The Editor urgently requests correspondents to hi ep their letters as 

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

 IS impossible otherwise to ensure the appearance even of com- 

 munications containing ititeresting and novel facts.^ 



Black Sheep 

 The following extract of a letter from Mr. Sanderson of 

 Chislehurst, \\\\o permits me to publish it, seems worth placing 

 on record. It relates to tlie former fie]uent appearance of spctted 

 or black sheep in the Australian flocks, as long as animals thus 

 coloured were of use to man, although they were never, as far 

 as Mr. Sanderson know--, separately bred from, and certainly 

 not in his own case. On the other hand, as soon as coloured 

 sheep ceased to be of use they were no longer allowed to grow 

 up, and their numbers rapidly decreased. I have elsewhere 

 assigned reasons for the belief that the occasional appearance of 

 dark-coloured or piebald sheej) is due to reversion to the primeval 

 colouring of the species. This tendency to reversion appears to 

 be ^most difficult quite to eradicate, and quickly to gain in 

 strength if there is no selection. Mr. Sanderson writes: — "In 

 the early days before fences were erected and when shepherds 

 had charge of very large flocks (occasionally 4C00 or 5000) it 

 was important to have a few sheep eaily noticed amongst the 

 rest ; and hence the value of a certain number of black or partly 

 black sheep, so that coloured lambs were then carefully pre- 

 served. It was easy to count ten or a dozen >uch sheep in a 

 flock, and when one was missing it was pretty safe to conclude 

 that a good many had strayed with it, so that the shepherd really 

 kept count of his flock by counting his speckled sheep. As 

 fences were erected the flocks were made smaller, and the 

 necessity for having these spotted sheep parsed away. Their 

 wool also being of small value the practice soon grew of killing 

 them off as lamb=, or so young t'oat they had small chance of 

 breeding, and it surprised me liow at the end of my sheep- 

 farming experience of about eight years the percentage of 

 coloured lambs produced was so much smaller than at the 

 beginning. As the quantity of coloured wool from Australia 

 seems to have much diminished, the above experience would 

 appear to be general." Charles Darwin 



The Nature of the Chemical Elements 

 Dr. Armstrong's article in Nature, vol. xxiii. p. 141, has 

 brought to my mind some calculations I made more than a year 

 ago to test a theory I had lo]ig previously entirtained. Most of 

 us who have paid much attention to the subject are agreed that 

 the elements are capable, under exceptional circumstances, of 

 profound chemical change. Mr. Lockyer is searching, with 

 success as it appears, for contemporary evidence of this by ex- 

 amining the condition of the solar surface. The other line of 

 evidence is historical, and turns mainly on the classification of 

 the numerical values of chemical symbols. It is of course only 

 with the latter that I have to deal. 



The classifications proposed by Nendands and Mendelejeff are 

 comprehensions of much similar preceding work. They appear 

 to me to be faulty in two ways : (i) on account of the seriously 

 large number of elements they wholly fad to include, and {2) 

 because of the strong stress they lay upon arithmetical series 

 of a rough /tT saltum character. As I do not know of any real 

 case of per saltum chemical change, I do not think the ele- 

 ments should be classified on such a basis. What is wanted 

 is a .system capable of including — with exactness and not 

 mere approximation — the w hole of the elementary num- 



bers ; that system to be represented in the mathemati- 

 cal symbols of ordinary chemical change, and therefore 

 free from a per saltum character. I have to a great 

 extent succeeded in finding such a system, and the results 

 of testing it at many points are as follow : — i. There is pro- 

 bably only one fundamental form of matter ; and this, as has 

 been previously supposed, yields our ordinary elements and many 

 others by ordinary polymerisation. 2. Almost all the elementary 

 numbers have been tried, and, with the exception of H and CI, 

 which are a little troublesome, they fall into order very exactly. 

 3. This order exhibits no discontinuity, and is similar to a case 

 of ordinary chemical change. 4. There is clearly an upper limit 

 to this order ; in other words, elementary numbers of more than 

 a certain magnitude appear to be impossible. 



Sir B. C. Brodie's method is really a classificatoi-y one ; and 

 I with others had been very desirous to read the Third Part of 

 the Calculus, in which it was promised ampler play. It will be 

 a matter for much regret if his premature death should have pre- 

 vented this. But w hat he did publish w as sound and sure : the 

 first real symbols chemistry has yet enjoyed, and the only ones 

 hitherto proposed w hereby the process and the results of chemical 

 change admit of unitary as well as kinelical representation. 



Edmund J. Mills 



Smokeless London 



As I hope soon to have an opportunity of reading a paper on 

 this subject before a scientific audience I need not occupy your 

 valuable space by replying to your correspondents of last week in 

 detail. 1 may say however that the scheme has been carried out 

 in practice at a gas-wcrk to which I shall afterwards refer. 

 When it w^as found that the apparatus for making gas on an 

 extraction of six hours was insufficient for supplying the wants ot 

 the long winter evenings the distillation was stopped w hen ga ; 

 had been removed to the extent of 5000 cubic feet per ton. The 

 larger quantities obtained from the coal per unit of time and the 

 superior illuminating power obtained per unit of volume tided 

 over the difficulty and rendered the existing plant sufficient. 

 No practical obstacles were discovered in discharging the 

 retorts. I do not think the difference between an extrac- 

 tion of 5000 and 3333 cubic feet per ton would make a 

 material change in this respect. Mr. Mattieu Wdliams points 

 out a much more serious obstn.iction in the plethoric indifference 

 of the gas companies. In reply to E. U. F. I may say that the 

 fuel resulting from a uniform extraction of 3333 cubic feet per 

 ton is practically smokeless if it is taken hot from the retorts and 

 immediately quenched with water. 



Westminster, December 27 W. D. Scott-Moncrieff 



Colliery Explosions and Coal-Dust 



Accepting Mr. Galloway's view that in many mines the 

 extent and destructiveness of colliery explosions are due to the 

 distribution of coal-dust in the air, may I suggest the possibility 

 of preventing the explosion from spreading beyond the sphere of 

 the fire-damp by sprinkling the floors throughout, at certain 

 regular interval-, with mineral oil ? A shady road, with one 

 such sprinkling, may be kept free from dust for several weeks 

 during the summer, and the corridors of a mine, not being open 

 to wind and rain, w ould of course remain wet for a longer jieriod. 

 A saucer filled with dust and treated with mineral oil w ill retain 

 the oil for months even when expo-ed to sun and rain. The 

 mixture of coal dust and oil is quite uninflammable. The experi- 

 ment may perhaps be w'orth trying in one of the drier coal-mines. 



December 27 R. RussELL 



Geological Climates 

 Prof. Duncan is under the impression that the claim of 

 Araucaria Cunninghami to have flourished at Bournemouth 

 during the Eocene, rests on "a bit of a leafy part of a tree," 

 and that this hit is "squashed." The foliage is however 

 abundant there, occurring almost wherever vegetable remains 

 are found, from the east of Bournemouth Pier to half a mile 

 beyond Boscombe. In one place, where a bluff is literally full 

 of it, the di- articulated branchlets are perfect, and not in the 

 least decree compressed. Again, the determination was not 

 made by°Prof. Ilaughton, but rests upon my statement that this 

 foliage and that of -■/. Cunninghami cannot be distinguished 

 one from the other. That it is Araucarian foliage I am per- 

 fectly satisfied ; but whether the existing Australian species is 

 identical and unmodified, must remain doubtful until other 



