324 



NATURE 



[Fed. 24, 1876 



written narrative of Australian discovery interesting. Mr. 

 Eden has told the story attractively, and the reader will 

 not only be greatly interested, but will have a fair idea of 

 what has been done to extend our knowledge of the 

 " fifth continent " from its first discovery down to the 

 trans-continental journeys of Warburton and Forrest — 

 the latter, however, being referred to in a sentence or two. 



LETTERS TO THE EDITOR 



\_The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications.^ 



Dr, Bastian and Prof. Tyndall on Spontaneous 

 Generation 



I BEG you to allow me a few lines to protest, as Prof. Tyndall 

 has done elsewhere, against Dr, Bastian's proceeding, in citing a 

 number of observers in support of his views (Nature, vol. xiii. 

 p. 284), whose researches taken in each case — as a whole — furnish 

 conclusive arguments against his views. 



It is only by an inadequate statement that the observations of 

 Dr. Pode-and myself — which appear in Dr. Bastian's list — can 

 have this signification attached to them. Where we obtained the 

 result which Dr. Bastian obtained, we were able to trace it to a 

 vitiation of the experimental conditions. Our results conclu- 

 sively and categorically contradicted the particular assertions 

 contained in Dr. Bastian's book, the " Beginnings of Life," into 

 the truth of which we set ourselves to inquire. 



Feb, 16 E. Ray Lankester 



Radiometers and Radiometers 



I HAVE recently been trying some experiments with a radio- 

 meter, obtained from Mr. Browning, and as some of my results 

 are different from what I was led to anticipate, I should 

 like to know whether there is anything special in my particular 

 instrument, or whether other people have noticed the same 

 things. 



In Mr, Crookes' paper on ** The Mechanical Action of Light," 

 Quarterly Journal of Science, No. xlvii. p. 348, he states that 

 * ' when only dark heat is allowed to fall on the arms [of the 

 radiometer], as from a vessel of boiling water, no rotation what- 

 ez'cr is produced." (The italics are mine.) 



Now I find that my radiometer is particularly sensitive to 

 dark heat, the presence of a heated copper wire, or still more 

 that of an iron poker when only slightly warmed, instantly 

 accelerating the number of revolutions. 



But more than this : when exposed in a room to diffused day- 

 light, the velocity of rotation is greatly influenced by the tempe- 

 rature of the room, and is by no means an indicator of the 

 amount of light only. 



One morning this week during the frost, upon looking at my 

 i-adiometer, it appeared to be motionless, although standing not 

 far from my study window. When placed nearer to the light it 

 revolved, but so slowly that I thought the instrument must have 

 received an injury. The room at the time was very cold, as the 

 fire had not been lighted. After the fire had been lighted and 

 the temperature of the room raised, the velocity of rotation 

 increased, and upon observing the instrument just before dark, 

 whe.i the room was very warm, the rotation was considerably 

 greater than it had been in the window in the middle of the 

 day, although at the time there was only just enough light in the 

 room to enable me to see the instrument at all. When I brought 

 the radiometer near to the fire, which consisted only of dull 

 hardly glowing coals, the rotation of the arms became so rapid 

 as to render them almost invisible. 



Upon taking the instrument out of doors between five and six 

 o'clock in the afternoon, the thermometer a few degrees below 

 freezing-point, the arms revolved slowly from right to left as 

 usual, but upon bringing it near to a mass of snow, and shading 

 the light off by some pieces of wood, I could see that the arms 

 revolved slowly in the opposite direction, that is, in the same 

 direction as the hands of a watch. Later in the evening I held 

 the instrument in the open air in bright moonlight, the thermo- 

 meter being at 24" F., and the rotation was again in the same 

 direction as the hands of a watch. The next morning, when the 

 temperature was nearly the same, but the air foggy with only 

 feeble light, the arms revolved at about the same rate but in the 



usual direction, from right to left. In the evening I again held 

 the radiometer in the moonlight in the cold frosty air ; the rota- 

 tion was as before, from left to right. Carrying the instrument 

 in my hand I approached the house, the hall door of which stood 

 open. As I came within reach of the light and heat the 

 rotation diminished, and at length ceased, but upon entering the 

 hall it commenced again, only in the opposite direction. In fact, 

 I could stand in such a position that upon moving a few feet 

 either way, I reversed the direction of rotation, while between 

 the two there was no motion at all. 



I afterwards repeated the experiment in a different form. I 

 placed the instrument in a cupboard in a very cold room, with a 

 considerable quantity of ice. Upon just opening the cupboard 

 door and peeping in, I could see that the arms were revolving 

 very slowly, but distinctly, from left to right. Upon opening 

 the door a little wider the motion ceased, and when still more 

 light was admitted the motion was reversed. 1 then removed 

 the ice and nearly closed the door— the rotation ceased entirely ; 

 but upon introducing a piece of heated iron the arms spun round 

 as fast as they usually do in full sunlight, and this, be it remem- 

 bered, when the cupboard was almost dark, the door being only 

 just sufficiently open for me to see the instrument, certainly not 

 more than a quarter of an inch. T. N. Hutchinson 



Rugby, Feb. 12 



Since writing the abave, I have been favoured with a note 

 from Mr. Crookes, in which he points out to me that h's results 

 have been obtained by means of radiometers constructed with 

 pith discs, and having no metal at all in the moving parts. In 

 the little instrument that I have used the discs are of mica, 

 blackened, of course, on the alternate faces, but mounted upon 

 four metallic arms, apparently aluminium foil. Mr. Crookes 

 observes: "I long ago gave up metallic instruments owing to 

 their erratic movements while radiating or absorbing heat. I 

 have mentioned this peculiarity of metallic radiometers in my 

 papers for the Royal Society. " 



As this difference between the instruments used accounted, to 

 some /extent, for my obtaining results so different from those 

 described by Mr. Crookes in the paper referred to, I felt at first 

 that there was no further need to trouble you with these remarks, 

 and that they had better be consigned to the waste paper basket. 

 Upon second thought", however, it seems to me that there is 

 still something that requires explanation, or, at all events, that 

 I do not understand, in the different action of dark heat on pith 

 only, and on mica mounted on thin metallic arms. The four 

 arms are very fine, equally bright, and similar in all respects, 

 hence it is difficult to see how rotation should be produced by 

 the action of heat on the metallic parts of the apparatus. The 

 vacuum, no doubt, is not so perfect as that obtained by Mr. 

 Crookes with his exquisite Sprengel pump, but even this would 

 hardly account for the "erratic movements" that I have 

 observed. 



I may add that since performing my experiments I have 

 learnt that one of my pupils in Rugby School, Mr. H. F. 

 Newall, has observed very similar results with a radiometer in 

 his possession. T. N. H. 



The Sailing Flight of Birds 



Having had during several long voyages in the Pacific con- 

 siderable opportunities for observing closely the flight of sailing 

 birds, and especially of Diomedea Melaiwphrys, or "Mutton 

 Bird," as I believe it is called by the Australians, a few sugges- 

 tions on the subject may perhaps not be uninteresting to your 

 readers. 



This bird^differs considerably in size from the albatross of the 

 Cape, but as the principles of its flight are the same, the few 

 suggestions I wish to make will apply with equal force to both 

 species, and indeed to all sailing birds. 



The Diomedea of the Cape it is well known can support itself 

 in the air for a very long time without flapping its wings, and in 

 "The Reign of Law " it is stated that "sometimes for a whole 

 hour together this splendid bird will sail or wheel round a ship 

 in every possible variety of direction, without requiring a single 

 btroke of its pinions." This may be accurately true, but in the 

 case of the smaller albatross I refer to, between one and two 

 minutes, or perhaps 1,000 or 2, coo yards in space, is more approxi- 

 mately the limit to which the bird's power of saUing is exercised. 

 When the flight begins after rest the bird appears to feel very 

 considerable difficulty in lising from the sea. It runs along the 

 I surface for some distance, flaps its wings very vigorously, and 

 continues to do this after it has left the water, until it acquires a 



