NOTES. 



ASTRONOMY. 



By A. C. D. Crommelin. B.A.. D.Sc, F.K.A.S. 



BOTAXV 



Bv Prokessor F. Cavers. D.Sc F.L.S. 



Being at the seaside and away from all sources of 

 astronomical information or reference my notes this month 

 are very brief. 



EN'CKE'S COMET was found on the last day of July, by 

 M. Gonnessiat, at Algiers. Owing to its unfavourable position 

 there were some apprehensions that it might escape detection 

 at this return, and thereby break a remarkable record of 

 visibility at every return since 1819. Perihelion is passed 

 about August 20th. After the observations of this return 

 have been discussed, it will be possible to discriminate between 

 Professor Backlund's two hypotheses to explain its recent 

 movements, viz. : II) that it suffered a sudden change in its 

 rate of acceleration about 1905, (2) that the mass of Mercury 

 which he had previously derived is sensibly in error. Encke's 

 comet affords the best way of determining the mass of 

 Mercury, since the two bodies are periodically very near 

 together. None of the planets are sufficiently perturbed by 

 Mercury to give its mass with any accuracy. 



BROOKS' COMET.— After last month's notes were 

 written, the veteran comet discoverer, Mr. \V. Brooks, of 

 Geneva, U.S.A., discovered a faint comet, which is likely to 

 brighten into naked eye visibility before next November, when 

 it makes a fairly near approach to the earth. The earth, 

 about September 3rd, will pass through the point occupied by 

 Kiess' comet four weeks earlier. There is a possibility of a 

 meteor shower at that date, if the comet has a meteoric 

 appendage following in its wake, as some comets are knoun to 

 have. 



SOLUTIONS TO MR. BARTRUM'S QUERIES (page 

 311). — The answer to the first query. ;v the iUuniination of 

 Venus, is that his law of illumination, varying as the cosine of 

 the angle of incidence, only holds for smooth spheres, which 

 the planets are not. Even tiny inequalities on the surface, far 

 too small to be discerned from other planets, suffice to give 

 an altogether different law of illumination. 



The most casual glance at the Moon suffices to show that 

 the illumination at the terminator is very different from zero, 

 which it would be on his hypothesis. The actual law is doubt- 

 less a very complicated one. but empirical formulae have been 

 given for representing observed facts with fair approximation. 

 The formula used in the Xautical Almanac for finding when 

 Venus is brightest is avowedly only a rough approximation, and 

 does not profess to accurately represent the facts of nature. 

 It is only used because the phenomenon is not considered a 

 sufficiently important one to call for a refined investigation ; 

 indeed it would be practically impossible to determine 

 by observation the average slope of the small inequalities on 

 its surface, which would be one of the necessary data of an 

 accurate solution. Re his second query, the phrase " mean 

 distance," if used without further qualification, is always 

 taken to mean the semi-major axis of the elliptical orbit. 

 If any one desires to use the phrase in one of the other 

 meanings which he indicates, it is necessary to specially state 

 the fact. 



I prefer to postpone his third query till next month. I 

 think I see the fallacy involved, but it is easy to make mistakes 

 in such problems. In any case, he has succeeded in finding a 

 neat little astronomical catch. 



PRE-GLACIAL FLORA OF BRITAIN.— In a recent 

 paper on the plant remains found in the Pre-glacial deposits of 

 Norfolk and Suffolk. Clement Reid ijoiini. Linn. Soc.) gives 

 a list, with notes, of the Fre-glacial species of British flowering 

 plants now known, numbering one hundred and fifty. The 

 plants described grew in the small stream channels of a large 

 river, probably the Rhine, and in the adjoining wet meadows 

 or in moist woods close at hand. The flora of Norfolk and 

 Suftblk as a whole has altered very little in the many thousands 

 of years since these beds were formed, although it was driven 

 out by the cold of the Glacial Period and returned later. 

 A certam number of exotic species are recorded, however, 

 these including three species of Ranunculus, a. water lily, the 

 water-nut iTrapa uatansK the spruce fir iPicea c.xcclsa), 

 and Naias niitior. The southern element in the Cromer 

 flora is therefore greater than was formerly supposed, and it 

 apparently includes several extinct species. These pre- 

 glacial plants suggest climatic conditions almost identical with 

 those now existing, but slightly warmer — a difference doubtless 

 owing to the fact that Britain was then united with the 

 Continent. 



THE FUNCTIONS OF LATEX.— In a very large 

 number of flowering plants, there are special sacs and tubes 

 containing the juice called latex, which is conmionly milk-like 

 in appearance {e.g. in dandelion, spurge, sow-thistle), but may 

 be colourless, or red. or orange in colour. Latex contains a 

 great variety of substances (e.g. proteins, starch, rubber, 

 alkaloids), and its uses to the plant have been much discussed. 

 Some writers state that latex is mainly, if not entirely, 

 composed of waste substances, which do not enter again into 

 the metabolism of the plant, though useful in guarding against 

 the attacks of animals, on account of the bitter and poisonous 

 substances they contain. Others contend that latex is largely 

 made up of reserve food materials, which are e\C3tually used 

 up in the nutrition of the plant. 



The most recent contribution to the controversy is a paper 

 by Bernard (Annales dit jard. hot. dc Buitenzorg. 19101, in 

 which some interesting new facts are gi\-en. This writer 

 supports the view that latex functions largely as a depository 

 of reserve food materials. He finds that the fruits of various 

 latex-containing and rubber-yielding plants have abundant 

 thick latex when young, whereas the ripe fruits contain very 

 scanty and thin latex. This he regards as proof that the 

 substances present in latex are used up in the formation of the 

 fruits and seeds, after being converted into other food 

 materials. He also shows that when spurges are cultivated in 

 air deprived of carbon dioxide, so that they cannot manufacture 

 carbohydrate foods from external sources, the starch grains in 

 the latex are corroded and are apparently changed into sugar 

 for the nutrition of the plant. 



.ACIDITY OF BOGS. — ,As is well known, the peat-moss 

 [Sphagnum I rarely grows on limestone soils. Some years ago, 

 it was shown by Paul that calcium carbonate is very injurious 

 to Sphagnum, even in small quantities. He grew various 

 species in water containing lime and found that the plants 

 soon perished. He found that not all salts of lime have an 

 equally injurious effect, and that alkaline salts of potassium 

 and sodium are as deleterious as those of lime. Various other 

 writers have found that peat-mosses give an acid reaction ; 

 hence it has been suggested that the injurious effects of lime 



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