December 29, 1904] 



NA TURE 



If the law of radiation pressure can be taken as still 

 holding when the radius is reduced to a = io-^, the acceler- 

 ation is 2 cm. /sec.-. This implies that such a particle of 

 dust, in a vacuum, and between vertical walls respectively 

 at 27° C. and 127° C. would not fall vertically, but would 

 deviate about 2 mm. per metre towards the colder wall. 



The effect found by Prof. Osborne Reynolds (Phil. Trans., 

 ii., 1879, p. 770) on a silk fibre exposed to radiation from 

 a hot body, and assigned by him to " radiometer " action, 

 is far larger than this. The radius of the fibre was 

 0000625 cm., and its length was probably about 15 cm. 

 When it was hung up in a test tube containing hydrogen 

 at atmospheric pressure, and was exposed to radiation from 

 a neighbouring jar filled with boiling water, the lower end 

 of the fibre moved through o 01 cm. This would imply an 

 acceleration of about 07 cm. /sec.',- about sixty times the 

 acceleration on a dust particle of the same radius under the 

 conditions assumed above. The action detected by Reynolds 

 increased, too, very rapidly as the pressure fell, being ten 

 times as great when the pressure was reduced to i inch of 

 mercury. J. H. Povnting. 



The University, Birmingham, December 15. 



The Date of Easter in 1905. 



Already queries have been addressed to me on the subject 

 of the date of Easter in 1905, owing to the fact that, accord- 

 ing to the almanacs, the moon is full at 4h. s6m. Green- 

 wich mean time on the morning of March 21 next, and that 

 therefore, according to the Prayer Book rule, it would 

 appear that Easter Day should be the Sunday following 

 March 21, viz. March 26. As the misunderstanding on the 

 subject seems widely spread, perhaps you will allow me to 

 explain that the " moon " referred to in the ecclesiastical 

 calendar is not the actual moon in the sky, which is full 

 at a definite instant of time, but a fictitious moon, the times 

 of the phases of which are so arranged as not to differ much 

 from those of the actual moon. These phases are held to 

 occur, vaguely, on certain days, and therefore hold good 

 for all longitudes, and so avoid a practical inconvenience 

 that would arise from the use of the actual moon. Thus, in 

 the instance before us, in which the actual moon is full at 

 4h. 56m. a.m. Greenwich mean time, the same moon is 

 full at iih. 48m. p.m. (on the preceding day) Washington 

 mean time. The people adopting Greenwich time would, 

 therefore, in the supposed circumstances, keep Easter Day 

 on March 26, whilst those adopting Washington time would 

 keep it on April 23. 



Perhaps the simplest expression for the date of the Paschal 

 full moon is March (44 — epact), which gives the date 

 directly when the epact is less than 24. When the epact is 

 equal to or greater than 24, this expression gives the date 

 of the preceding full moon, and the Paschal full moon is 

 found by adding 29 to this date. 



Thus in 1905 the epact is 24, therefore the calendar moon 

 is full on March 20, and again on April iS. The latter is, 

 by the rule, the Paschal full moon, and Easter Day is the 

 following Sunday, viz. April 23. 



A. M. W. Downing. 



H.M. Nautical Almanac Office. 



Lepidocarpon and the Gymnosperms. 



The concluding sentence in your note on Mr. H. E. H. 

 Smedley's admirable models of the fructifications of 

 Palaeozoic plants (N.\ture, December 22, p. 183) may 

 possibly be misleading to some of your readers. As the 

 models of Lepidocarpon shown in your figure were pre- 

 pared from my instructions, I may be supposed to share 

 the responsibility for the hypothesis of an affinity between 

 the lycopodiaceous cones and the Gymnosperms, stated to 

 have been urged by " the author," especially as the points 

 of agreement mentioned are quoted, with some slight 

 abridgment, from my paper on the seed-like fructification 

 of Lepidocarpon in the Philosophical Transactions.^ Such 



' ^''.'.(- ^'■'""- R.S., Series B, vol.cxciv., 1901, p. 320. See also Nature, 

 vol. Ixiii., 1Q00-1901, pp. 122 and so6. 



NO. 1835, VOL. 71] 



an aflinity has never appeared to me to be probable. The 

 characters cited — the presence of an integument and micro- 

 pyle, the single functional megaspore, and the detachment 

 of the indehiscent, seed-like organ as a whole — are im- 

 portant points of analogy with true seeds, but in Lepido- 

 carpon " these organs differ too much in detail from the 

 seeds of Gymnosperms to afford any evidence of affinity."' 

 I doubt whether my friend Mr. Smedley really intended 

 to suggest anything more than an analogy. 



As regards the Gymnosperms, evidence has been accumu- 

 lating for some time past indicating their connection with 

 the fern-phylum rather than with the Lycopods. Some 

 account of this evidence will be found in my discourse at 

 the Royal Institution on the origin of seed-bearing plants 

 (1903)," while a more recent summary is given in Mr. 

 Arber's article on Paleozoic seed-plants in X.'iTURE for 

 November 17, p. 68. 



The seed-like organs of some Palaeozoic Lycopods, such 

 as Lepidocarpon and Miadesmia,' seem to be cases of homo- 

 plastic modification, and not to be indicative of any affinity 

 with those groups of seed-plants which have come down 

 to our own day. D. H. Scott. 



Jodrell Laboratory, Kew. 



Fishing at Night. 



The notice in your Journal of the " Sea Fishing Indus- 

 try," written by Mr. Afialo, suggests to me that he or some 

 other of your readers may inform me why sea fishing takes 

 place for the most part at night. I have heard the subject 

 discussed all my life, and the answers have been of the most 

 opposite and unsatisfactory character, such as to obtain a 

 supply of fish for the morning markets, and because fish 

 come nearer to the surface in the dark. Everyone must be 

 familiar with the sight of our fishing boats preparing to 

 take their departure as the evening approaches in the 

 dilTerent harbours on our coasts. Some of the masters, 

 unfortunately, like the Apostle Peter, have toiled all night 

 and caught nothing. S. W. 



December 20. 



A New British Bird ! 



A FINE example, a male, of the Pacific eider-duck, Soma- 

 teria v-nigrum, was killed at Scarborough on December 16. 

 This is the first recorded instance of the occurrence of this 

 bird on our shores. Closely resembling the common eider, 

 Somateria molissima, it may yet be readily distinguished 

 therefrom by the bright orange colour of the bill, and the 

 sharply defined, black V-shaped mark on the throat — hence 

 the specific name v-nigrum. 



The Pacific eider occurs in abundance along the coasts 

 of north-western America and north-eastern Asia. 



W. P. Pycr.'VFT. 



Natural History Museum, South Kensington. 



Intelligence of Animals. 



In reference to the question of intelligence in animals, it 

 may be of interest to mention a case of distinct reasoning 

 power in a cat which for nine or ten years associated him- 

 self with our family ; he would have scorned the suggestion 

 that he belonged to it. When he found himself on the wrong 

 side of a closed door — a very constant occurrence — he stood 

 up and, catching the handle in his fore paws, rattled it. 

 I do not think he tried to turn the handle, but he certainly 

 knew that it played an essential part in the opening of the 

 door. He is now no more, and de wortuis nil nisi bonum 

 bars any further reference to his career, for he was a dissi- 

 pated old scoundrel ; but it is a pleasure to me to pay, with 

 your permission, the above little tribute to his memory. 



Greenock, December 17. T. S. P.«ters6n. 



1 P/iil Trans., loc. cit, p. 324. 



- Natirk, vol. Ixviti., p. 377. 



■J Miss M. Benson, "A New Lycopodiaceous Seed-like Organ," Nett^ 

 Phytoloirist, vol. i., 1907, p. 58. 



