May 2, 1872] 



NATURE 



distribution of leaves around the stem. The latter part of 

 this valuable paper consists of an attempt to show that 

 the modes of phyllotaxy which result from the use of the 

 different forms of the fraction are either directly serviceable 

 to the plant by affordin'j the best distribution, either for 

 absorbing the sap from the roots or for exposing it to the 

 action of air and light, or have been so at some period of 

 the ancestry of the plant, when its structure was of a 

 simpler character. The typical or unique angle of the 

 theory of phyllotaxy the author regards to be the goal 

 towards which the special forms tend, by the action of the 

 principle of natural selection, rather than as the origin of 

 the spiral arrangements. A. W. B. 



LETTERS TO THE EDITOR 



[ The Editor does not hold himself responsible for opinions express;,! 

 by his correspondents. Ko notice is taken of anonymous 

 communications. ] 



The Law of Total Radiation 



In Nature for April 25 Captain Ericsson attacks the calcula- 

 tion of Pouillet as to the sun's temperature, as being founded on 

 an erroneous law of radiation. Had he contented himself with 

 saying that the exten.sion of Dulong and Petit's law so far 

 beyond its experimental foundation to temperatures approaching 

 that of the sun was " mere theory," and mconsis'ert with his 

 own experiments, his position mii^ht have been impregnable. 

 But not satisfied with this, he goes on to question the applica- 

 bility of Dulong's law even below the boiling point of mercury, 

 and asserts that Xewton's law is much nearer the truth. The 

 only objection that he gives to the method of the French ex- 

 perimenters is that they erroneously confuse the surfue tem- 

 perature of their tliermometers with the average temperature of 

 the contained mercury. The observed radiation is really due to 

 the first, though attributed to the second. Now, without assert- 

 ing that the objectim is entirely without force, I submit that, if 

 Newton's be the real law of radiation, it is impossible in this 

 w.iy to account for the observations. 



In the first place, if the rate of cooling for a body at a variable 

 temperature /, surrounded by another at a fixed temperature t^, 

 be proportional to / — /„, it follows from the theory of exchange 

 (than which there are few things better established) that the 

 radiation between two bodies at any temperatures t, t', is propor- 

 tional to / —;'. The rate of cooling of the thermometer con- 

 tained in an enclosure would thus depend only on the excess of 

 temperature, in flat contradiction to Dulong's observations. Nor 

 would this result be altered, even though the material of the 

 thermometer were so badly conducting in relation to its size as to 

 allow the surface temperature to fall considerably below that of 

 the interior. Whatever may be the relative temperatures after a 

 given time of asystem composed of a conducting mass, originally 

 at a uniform temperature of 100", surrounded by an enclosure 

 maintained at o", the same after the same time will be the 

 differential temperatures of the corresponding parts of another 

 similar system, whose interior mass had originally a uniform 

 temperature of 200°, with a case maiutained at 100°. In fact, 

 according to Newton's law, and with a constant conductivity, 

 the superposition of any constant temperature over the whole 

 system alters none of the conditions. 



If it be objected that in the interior of a thermometer heat is 

 distributed, not merely by conduction, but is convected by cur- 

 rents in the mercury, even this, I believe, will make no difference. 

 The convection currents are a consequence of differences of 

 density, and these are approximately proportional to the 

 differences of temperature. The addition of a constant tem- 

 perature to the whole alters nothing. 



Judgingfrom the evidence at present before us, it is impossible 

 to avoid the conclusion that within the limits of Dulong's experi- 

 ments Newton's law of cooling cannot be even approximately 

 true. If Capt. Ericsson, by bringing forward fresh experiments, 

 and by proving the fallacy of old ones, can establish the truth of 

 Newton's law, he will lay Science under a great obligition. 

 Speaking as a mathematician, I could even wish him success. 



With regard to high trm eiaturrs it seems crrtain that Dulong 

 and Petit's law fails ; for it is impossible to believe that the sun 



is no hotter than 1,500° Cent., at least if the estimates hitherto 

 made of terrestrial temperatures are substantially correct. It 

 must be remembered, however, that according to Fizeau the sun 

 is only about 2\ times brighter than the eleciric arc, which does 

 not even imply a higher temperature ; because, while the sun 

 must give us nearly the whole radiation due to his temperature, 

 the electric arc is probably transparent, 



J. W. Strutt 

 Terling Place, Witham, April 29 



Solar Halo 



This morning, at 9.20, I observed a strongly-marked halo 

 round the sun. Roughly extemporising a sextant with a post- 

 card and paper-vector, I took three observations on the semi- 

 diameter, and found the mean to be 22'''6. So I conclude this 

 to be the ice-halo, whose deviation is 23°, being formed of 

 hexagonal crystals. Two facts render the halo noteworthy — (i) 

 the morning (after a heavy gale from the south) was exceptionally 

 warm ; (2) the halo exhibited the extreme colours in the proper 

 order. I am told halos do not exhibit colours. Surely they 

 ought to ; and if not, why not ? Let some of your readers 

 au'^wer me this. The halo was visible till nearly 10 o'clock. 



Bournemouih, April 26 C. M. Ingleby 



Help us to save our Birds 



All praise be given to those who have made a stand for the 

 preservation of British birds. With a spirit of patience they 

 have had to encounter the crass prejudice that sometimes saturates 

 even the rufal mind, and to prove that if the small bird takes its 

 toll from, it also greatly assists in preserving the store of, the 

 farmer. They have had to combat the sporting instincts of the 

 excited townsman, so joyous with his escape from the smoky 

 labyrinths of his brick-built prison that even a feathered shuttle- 

 cock would almost seem like game. Last and greatest feat, they 

 have had to question the right to worship the national idol — ■ 

 gain, and to teach people, that even if, by the wholesale 

 slaughter of feathered tribes, some persons scraped up gold, still 

 that occupation, however praiseworthy, was against the general 

 good. Truth at last dawned on the mind of the people, and so 

 Parliament shielded, amongst other fowl, the pretty kittiwake 

 from destruction, and preserved fashionable women from one 

 more barbarism. 



Those who have thus worked to educate the public need not 

 rest on their oars for lack of employment, let them look farther 

 afield, let them fearlessly step across national boundaries, and 

 lend their strength to assist in arresting the impending destruc- 

 tion of many species of the most beautiful and interesting orders 

 of animated nature in any quarter of the globe. 



New Zealand, so long left by science to slumber on the calm 

 bosom of the Pacific, has disclosed, amongst her birds, forms that 

 have surprised the naturalist as much as they have excited the 

 speculation of the philosopher. The remains of birds, of orders 

 other than the gigantic Struhiones, giving us hints about strange 

 lost forms of animal life that have lingered in these islands, per- 

 chance, almost to our own times, are now and then exhumed 

 from the hidden shores of swamp and morass. We raise a cry 

 for help in behalf of the mass of birds that yet remain near us 

 (we had almost said with us), in the hope that the attention of 

 naturalists in Europe may be called to the peril of extermination 

 that hangs over many interesting indigenous species. For the 

 preservation of our birds we require some assistance from abroad, 

 our time is so crowded with occupations of many kinds, that with- 

 out some pressure from without, little attention would be likely to 

 be paid to the subject. This is said not without reason, not without 

 some experience ; in 186S, in Parliament, the writer tried to se- 

 cure the conservation of our magnificent forests, a resolution 

 was passed by the House to that effect, official inquiries were 

 made ; — nd I'ono ? Our forests are now being damaged and de- 

 stroyed, where not protected by climate, in so ruthless a manner, 

 that no further evidence is needed to prove our wasteful style of 

 settlement. Will not some one having authority in such matters 

 speak a word in due season for our birds ? I believe nearly every 

 living species that we number could be preserved with proper 

 care. If that is a fact, is it not interesting enough to naturalists 

 to induce them to stimulate us to efforts more likely to give 

 better results than our present legal enactments ? 



