10 



KNOWLEDGE, 



[J.UJUAEY, 1903. 



seeing as good nor as bad as it had been during some of 

 the observations made in 1898 and 1899, when the spot 

 was very much smaller. 



'• The' real explanation of the unusually large change in 

 the size of the spot," he continues, " I believe to be that 

 Linni' was more active than heretofore, and therefore that 

 there was more moisture about it to condense. 



'• A series of measures made on October 20, at 

 15h. 26ra., or 12'''6 after sunrise, gave a diameter of 

 4"61 : secingS in the standard scale. The seeing, as judged 

 bv the image of the moon, was clearly inferior to that at 

 any time during the night of October 1(3. The image of 

 Linnc was much larger than it appeared by any of the 

 measures made before the eclipse, and much smaller than 

 it appeared by any of the measures made after it. It 

 therefore appears that the sudden increase of size after 

 totality could not be due to inferior seeing. 



" It also appears that on or before October 20 the spot 

 had again begun to shrink in size, due, presumably, to 

 evaporation in the intense sunlight. Four measures of 

 the spot made in 1898, from 12'''4 to 13''7 after sunrise, 

 gave diameters of 3"'-52, 3"'24, 3"-42, and 3"-46 (Harvard 

 Annoh, XXXII., 206). The measui-es made on October 20, 

 1902, 4"'C)1, therefore confirms those of October 1-5 and 16, 

 in showing that the spot has increased in size during the 

 last three years." 



♦ 



llttttrs. 



[The Editors do not hold themselres responsible for the opinions 

 or statements of correspondents.] 



THE VISIBILITY OF THE CRESCENT OF VENUS. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — In the December issue of Knowledge is a letter 

 on the visibility of the crescent of Venus with the unaided 

 eye, with regard to which 1 should like to make a remark. 



At the time of the observation — the end of October or 

 beginning of November, 1901 — Mercury would, of course, 

 be a beautiful crescent. 



The writer of the letter points out the planet to two 

 naked-eye observers, and then they are shown the crescent 

 in the telescope. Their attention is the7i directed to a 

 similar object in proximity to that just examined. Now, 

 under the circumstances, perhaps it is not altogether 

 surprising that one of them should have the sagacity 

 (shall I call it) to infer that the " shape " would be " just 

 like the new moon." 



But the second part of the observation, referring to the 

 " rest of the star, the dark round we see," is beyond my 

 comprehension, and I should like to ask the writer if he 

 can kindly describe its appearance in the telescope. I 

 sup]5ose it had some reference to earthshine upon our 

 satellite. T. H. Astbuey. 



Croft Villas, Wallingford. 



HABITS OF SANITATION. 



TO THE EDITORS OF KNOWLEDGE. 



SiES, — I have read with much interest the article by 

 Mr. Cox on the " Domestic Economy of the Thrush." As 

 regards the sanitary habits of the thrush and other birds, 

 may I suggest that the i>ractice is much more common 

 than appears to be known, and was probably origiaallv 

 followed by all animals whose young are helpless and 

 incapable of locomotion. The domestic cat disposes of the 

 excreta of her young in the same way, and for the first 

 three weeks her nest is absolutely sweet and clean. 



M. S. S. 



Astronomical. — Fizeau's experiment for the determina- 

 tion of the velocity of light has recently been repeated on 

 an imposing scale by M. Perrotin, Director of the Nice 

 Observatory. The mean result of 1109 observations gives 

 the velocity in vacuo as 299,860 kilometres or 186,328 miles 

 per second. Taking the value 8"'S05 for the solar parallax, 

 as derived from observations of Eros, the theoretical value 

 of the constant of aberration is 20"465, which, it is 

 gratifying to find, is exactly that adopted by the 

 International Conference of 1896. — A. F. 



New Comet (1902 d). — A new comet was discovered on 

 December 2, and, though extremely faint at present, it 

 occupies a very favourable position for observation. Early 

 in December it was estimated as about magnitude 11^. 

 On January 1, 1903, the comet will be placed about nine 

 degrees west of the bright star Procyon, and a week later 

 may be found some eight degrees west of /3 Canis Minoris. 

 At this period the comet will be nearly three times as 

 bright as it was ou the night of its discovery. Its motion 

 is slow towards the north-west, and directed to the stars 

 in the western region of Gemini. The comet is well 

 visible during nearly the whole night, and promises to 

 remain in view for a considerable period, for according to 

 the elements of the orbit computed by Ebell at Kiel (Ast. 

 Nach., 3834), the perihelion passage will not take place 

 untU April 19 next.— W. F. D. 



Botanical. — It is probable, judging from the enquiries 

 occasionally made, that the interesting articles published 

 on the Mexican jumping bean are not generally known. 

 The beans (or seeds) are not iufrequently met with, being 

 distributed as curiosities remarkable in possessing the 

 power of motion. The cause of this motion was not 

 difficult to explain, for on cutting through the seeds, a 

 single whitish worm was found in each. This was the 

 larva of an insect to which the name of Carpocapsa 

 saltitans was given many years ago, but it was not till 

 1891 that Dr. Rose, of the United States National 

 Herbarium, was able to identify the plant which produced 

 the seeds, though it was known that it belonged to the 

 Spurge family (Euphorbiaceit). From the observations 

 made by Dr. Palmer while collecting plants in Mexico, and 

 from the specimens which were received from him, it was 

 concluded that the source of the jumping beans was a new 

 species of Sebagtiania, which Dr. Rose called S. PaJmeri. 

 This is a dia?eious shrub or small tree, with the usual 

 three-celled capsule of the order. Each cell contains a 

 subglobose seed about two lines in diameter. The larva is 

 supposed to be hatched from an egg deposited on the 

 outside of the capsule, which it penetrates while still very 

 young. It remains for a long jaeriod in the larva stage, 

 during which it feeds on the substance within the integu- 

 ments of the seed, nothing remaining but a thin light 

 shell, which on being detached readily responds to the 

 peculiar movements of the larva within. Usually the 

 seed.s are moved from side to side, but sometimes they are 

 made to jump short distances. The jumping bean insect 

 is closely related to the common apple worm (Carpocapsa 

 yomonella). It is known to attack the seeds of a second 

 species of Sebastiania (S.Priii(ilei),vih\\e an allied species 



