200 



'SCIENCE. 



[Vol. IV., No. 



word is not to be too rigidly interpreted. I am bound 

 to say tbat plates which he has obtained do really 

 show just such appearances as would be produced by 

 such a solar appendage, though they are very faint 

 and ghost-like. I may add further, that, from a let- 

 ter from Dr. Huggins, recently received, I learn that 

 he has been prevented from obtaining any similar 

 plates in England this summer by the atmospheric 

 haze, but that Dr. Woods, who has been provided 

 with a similar apparatus, and sent to the Biffelberg in 

 Switzerland, writes that he has 'an assured success.' 



Our American astronomer, on the other hand, at 

 the last eclipse (in the Pacific Ocean), observed cer- 

 tain phenomena which seem to confirm a theory 

 he had formulated some time ago, and to indicate 

 that the lovely apparition is an apparition only, a 

 purely optical effect due to the diffraction (not re- 

 fraction, nor reflection either) of light at the edge of 

 the moon — no more a solar appendage than a rain- 

 bow or a mock sun. There are mathematical consid- 

 erations connected with the theory which may prove 

 decisive when the paper of its ingenious and able 

 proposer comes to be published in full. In the mean 

 time it must be frankly conceded that the observa- 

 tions made by him are very awkward to explain on 

 any other hypothesis. 



Whatever may be the result, the investigation of 

 the status and possible extent of a nebulous envelope 

 around a sun or a star is unquestionably a problem 

 of very great interest and importance. We shall be 

 compelled, I believe, as in the case of comets, to rec- 

 ognize other forces than gravity, heat, and ordinary 

 gaseous elasticity, as concerned in the phenomena. 

 As regards the actual existence of an extensive gas- 

 eous envelope around the sun, I may add that other 

 appearances than those seen at an eclipse seem to 

 demonstrate it beyond question, — phenomena such 

 as the original formation of clouds of incandescent 

 hydrogen at high elevations, and the forms and 

 motions of the loftiest prominences. 



But of all solar problems, the one which excites the 

 deepest and most general interest is that relating to 

 the solar heat, its maintenance and its duration. For 

 my own part, I find no fault with the solution pro- 

 posed by Helmholtz, who accounts for it mainly by 

 the slow contraction of the solar sphere. The only 

 objection of much force is, that it apparently limits 

 the past duration of the solar system to a period not 

 much exceeding some twenty millions of years ; and 

 many of our geological friends protest against so 

 scanty an allowance. The same theory would give 

 us, perhaps, half as much time for our remaining 

 lifetime ; but this is no objection, since I perceive no 

 reason to doubt the final cessation of the sun's activ- 

 ity, and the consequent death of the system. But 

 while this hypothesis seems fairly to meet the require- 

 ments of the case, and to be a necessary consequence 

 of the best knowledge we can obtain as to the genesis 

 of our system and the constitution of the sun itself, 

 it must, of course, be conceded that it does not yet 

 admit of any observational verification. No meas- 

 urements within our power can test it, so far as we 

 can see at present. 



It may be admitted, too, that much can be said in 

 favor of other theories ; such as the one which attrib- 

 utes the solar heat to the impact of meteoric matter, 

 and that other most interesting and ingenious theory 

 of the late Sir William Siemens. 



As regards the former, however, I see no escape 

 from the conclusion, that, if it were exclusively true, 

 the earth ought to be receiving, as was pointed out 

 by the late Professor Peirce, as much heat from 

 meteors as from the sun. This would require the fall 

 of a quantity of meteoric matter, — more than sixty 

 million times as much as the best estimates make 

 our present supply, and such as could not escape the 

 most casual observation, since it would amount to 

 more than a hundred and fifty 1 tons a day on every 

 square mile. 



As regards the theory of Siemens, the matter has 

 been, of late, so thoroughly discussed, that we proba- 

 bly need spend no time upon it here. To say nothing 

 as to the difficulties connected with the establish- 

 ment of such a far-reaching vortex as it demands, 

 nor of the fact that the temperature of the sun's sur- 

 face appears to be above that of the dissociation point 

 of carbon compounds, and hence above the highest 

 heat of their combustion, it seems certainly demon- 

 strated, that matter of the necessary density could 

 not exist in interplanetary space without seriously 

 affecting the planetary motions by its gravitating 

 action as well as by its direct resistance ; nor could 

 the stellar radiations reach us, as they do, through a 

 medium capable of taking up and utilizing the rays 

 of the sun in the way this theory supposes. 



And yet I imagine that there is a very general sym- 

 pathy with the feeling that led to the proposal of the 

 theory, — an uncomfortable dissatisfaction with re- 

 ceived theories, because they admit that the greater 

 part of the sun's radiant energy is, speaking from a 

 scientific point of view, simply wasted. Nothing like 

 a millionth part of the sky, as seen from the sun, is 

 occupied, so far as we can make out, by objects upon 

 which its rays can fall : the rest is vacancy. If the 

 sun sends out rays in all directions alike, not one of 

 them in a million finds a target, or accomplishes any 

 useful work, unless there is in space some medium 

 to utilize the rays, or unknown worlds of which we 

 have no cognizance beyond the stars. 



Now, for my own part, I am very little troubled 

 by accusations of wastefulness against nature, or by 

 demands for theories which will show what the 

 human mind can recognize as 'use' for all energy 

 expended. Where I can perceive such use, I recog- 

 nize it with reverence and gratitude, I hope ; but the 



1 In an article on astronomical collisions, published in the 

 North-American review about a year ago, I wrongly stated the 

 amount at fifty tons. There was some fatality connected with 

 my calculations for that article. I gave the amount of heat due 

 to the five hundred tons of meteoric matter which is supposed 

 to fall daily on the earth with an average velocity of fifteen miles 

 per second as fifty-three calories annually per square metre, — a 

 quantity two thousand times too great. Probably the error 

 would have been noticed if even the number given had not been 

 so small, compared with the solar heat, as fully to justify my 

 argument, which is only strengthened by the correction. I owe 

 the correction to Professor LeConte of California, who called my 

 attention to the errors. 



