Oct. 4, 1877] 



NA TURE 



477 



The immediate source of attraction possessed by the flower 

 for its feathered visitants lies, I think, in the small insects which 

 resort to it, and not, at any rate usually, in their furnishing any 

 nectareous secretion which is palatable to the birds. For if the 

 latter visited the blossoms for the sake of the nectar they would 

 be perfectly acquainted by experience with its situation and 

 make no delay in going straight to it, whereas the habit of the 

 sun-birds and the flower-peckers also is rather to hover on 

 rapidly-vibrating wings a few inches in front of the opening of a 

 blossom, as if prying into its recesses in search of food, before 

 thrusting their beaks into t^.e corolla ; and ofien after thus 

 examinnig a lljwer they fly oflf to another without touching it at 

 all, having apparently satisfied themselves that the first one con- 

 tained no prey for them. A. II. EviCRETf 



N. Mindanao, July 23 



Heat Phenomena and Muscular Action 



On reading the article which appeared in Nature, vo' xvi. 

 p. 451, on the heat phenomena accompanying muscular 

 action, it has occurred to me to send the following problem 

 which is akin to the subject. 



If a man does work (say lifts a weight), the principle of the 

 conservation of energy teaches us that the potential energy — the 

 work done — (weight lifted) is at the expense of the man as a 

 magazine of foice, in fact that "virtue has gone out of him." 

 Now suppose a man lifis say a ton of bricks and deposits the bricks 

 one by one on the top of a wall six feet high, we can exactly 

 estimate the amount of work done, the energy rendered potential 

 and external, and if we knew also the extra amount of heat 

 radiated or otherwise carried off from his body — as most probably 

 the work would raise his temperature — we could exactly measure 

 the amount of energy the lifting of the brick cost him. 



Now suppose another man were to lift the bricks from the top 

 of the wall and deposit them gently — i.e., without concussion — 

 on the ground, it is evident that there is a certain amount of 

 potential energy disappearing, in fact that there is work being 

 absorbed by the man, of course appearing in some other form, 

 but the question is how ? This second man's work is of course 

 in one .^ense work, but in the stnse of producing external, 

 potential, or kinetic energ)', is not so, unless, perhaps, in heat. 



Strangely enough it follows that lifting down the brick ought 

 to make the man either radiate heat more, waste tissue Its', 

 digest food less, or in some other way account for the energy 

 absorbed by him. 



Generally I think the conversion of force by obstruction is not 

 alwajs so clearU traced as it might be ; in friction it is clear, as 

 also in the compression of elastic bodies, but in the instance 

 above, as also in the throttling of steam, it is not so clear. 



A. R. Moi.isoN 



Does Sunshine Extinguish Fire? 



I READ Mr. Tomlinson'sf aper(NATUKE, vol. xvi. p.36r)near 

 the time of its delivery, and was struck with the inconclusive cha- 

 racter of his experiments. W hat he attempted to obtain was the 

 condition of combustion in sunshine and combustion in darkness, 

 (tclc-ris paribus. But he left the avteris paribus entirely out of the 

 experiment, and actually used a dark cubbard (I believe this is 

 good spelling etymologically and phonetically), into which there 

 was no free influx of atmospheric air. Naturally his candles burnt 

 with inferior combustion there. I have for years together burnt 

 Newcastle coal, and no other; and for years together burnt 

 South Staffordshire coal, and no other ; and I say that sunshine 

 puts out a sea-coal fire and not a S.S. fire. The reason of this 

 is, I apprehend, not far to seek. In the Midlands it is the 

 prattice to keep a fire alive by a raker, or gathercoal. It 

 would be quite useltsi to attempt to do this with a sea-coal fire, 

 which goes out in a short time unless the cakes of coal be broken 

 up ; in a word, one has to watch a sea-coal fire ; and it must be 

 in every Londoner's experience, that such a fire is apt to elude 

 one at the last faint gleam from over reckless puking. Now, if 

 the sun is shining on the coal, that last faint gleam is invisible, 

 and the fire goes out as a matter of course. Sunshine puts out a 

 sea-coal fire by insidiously eclipsing the warning glimmer of ils 

 expiring embers. This, at least, is a vera causa. A priori I 

 Eh juld say that combustion would be less rapid in air raiefied 

 by sunlight than in air deprived of it ; but I do not believe 

 sunshine extingui.-hes a c0.1l fire in any other way than that I 

 have described. C. M. Ingleiiy 



Folkestone 



OUR ASTRONOMICAL COLUMN 



The Approaching Opposition of Iris.— The oppo- 

 sition of this minor planet in the present autumn affords 

 another favourable opportunity of determining the amount 

 of solar parallax on the method already successfully 

 applied by Prof. Galle, of Breslau, in the case of Flora. 

 The DcrliiiL'i- astronomisches JaJirhucIi for 1879 contains 

 a rough ephemeris of Iris for every twentieth day of the 

 year, but this being insufficient for the purpose in view, 

 wc subjoin places calculated from Prof. Briinnow's tables 

 of the planet, on the approximate formute explained in 

 his introduction ; the error of the tables being very 

 sensible at the present time, nothing would have been 

 gained by calculating in the accurate form. For the sake 

 of brevity the planet's positions are given for every fourth 

 day only, but they will be readily interpolated for the 

 intermediate dates. 



Iris.— .4/ Gnymuick Midni'hl. 



Iris will be in perihelion October 14-7, G.M.T., and nearest 

 to the earth on November 15, her distance at this time 

 being o 859 (the earth's mean distance from the sun being 

 taken as unity). Her intensity of light may be expected 

 to rather exceed that of a star of the seventh magnitude, 

 6-Sm. according to the Berliner Jahrbueh. 



The Outer S.^tellite of Mars.— This object is 

 still under observation at the Observatory of Paris. It 

 was also measured again by Mr. Common, of Ealing, 

 with his 18-inch silver-on-glass reflector on September 24, 

 the angle calculated from the elements whi.;h have been 

 given in this column differing from the observed angle 

 — 4°. An observation on September 13, by M. Borrelly 

 at Marseilles, presumed to apply to the satellite, must 

 refer to a faint star, the satellite at the time being in the 

 opposite quadrant. 



Binary Stars.— Dr. Doberck, of Markree Observa- 

 tory, continues his investigations on the orbits of the 

 revolving double stars. In No. 2,156 of the Astronomisehe 

 Nachrichten he has given provisional elements of 2 1768 

 and 2 31 21, the latter of which appears to be an object of 

 special interest from the shortness of the period of revo- 

 lution, which hardly exceeds that of the well-known 

 binary, f Herculis. Also elements of 2 3062, a star which 

 ■was the subject of a pretty complete calculation by Dr. 

 Schur in 1867. The results of the two discussions are 

 as follow : — 



