48 ASTRONOMICAL PHENOMENA AND PROGEESS. 



tent and finally die, away. In the comet of The awards will be subject to the following 

 b noticed the descent of the en ; ** ^ ^ ^ ^ ^ ^ ^ ^ 



lets discovered in each of the three years named, 



velopes on the nucleus; and Herschel and 

 Schroeter remarked the same peculiarity in the 

 comet of 1811. From these facts the author 

 thinks that, although Professor Tyndall s hy- 

 pothesis accounts for some of the phenomena, 

 vet the true theory is still to be discovered. 

 Mr Uuggins, in the Redo Lecture, delivered 



and only for such comets as are telescopic at time 

 of discovery, that is, invisible to the naked eye. 

 The comet must not have been before seen by an- 

 other observer, and must not be one whose appear- 

 ance could securely be predicted. 



2. The discovery must be communicated immedi- 

 ately, and without waiting for further observations, 



. 



at Cambridge in May, details his spectroscopic to t j h ' e j m p er ial Academy of Sciences, by telegraph 

 observations* on Winnecke's comet (II., 1868), if practicable ; and otherwise by the earliest post. 



comparison of 



spectrum' with that The Academy undertakes to transmit the news imme- 



f ; nd concludes there- 



from~tnYtYh*e7o~metary matter from which the 

 light comes is the luminous vapor of carbon. 

 To this theory it may be objected that the de- 

 gree of solar heat to which the comet was ex- 

 posed would be insufficient to convert carbon ^^^ _ 



into vapor. Mr. Huggins replies to this, that car- obgervat i ns of the discoverer suffice for the deter- 

 bon may possibly exist in an allotropic state, in mination of the orbit. 

 which it may be much less fixed, and so be capa- 

 ble of passin'g into vapor at a comparatively low 

 temperature. At all events, the matter which 

 emanatts from the nucleus, and is distinguished 



the plan 



and course of the comet must be given as exactly 

 as possible with the first notice. This first notice is 

 to be supplemented by such later observations as may 

 be made. 



4. If the discovery should be confirmed by other 

 observers the prize will not be awarded unless the 



5. The prizes will be awarded in the general meet- 

 ing of tho Academy held at the end of May of each 

 year. In case the first notice of a discovery arrives 

 between the first of January and the end of May, the 



final award of the prize will be deferred till the gen- 



by a blue tint, does give a light which the prism era i meeting in May in the following year. 



shows to be identical with that emitted by the 

 vapor of carbon ; therefore it is certain that 

 the light which has the blue color is not due 

 to reflection from a cloud, of which the parti- 

 cles are too small to reflect the longer waves of 

 its less refrangible colors. The invisible spaces 

 between the envelopes may possibly correspond 

 to a condition of the vapor too cool to emit 

 light, and yet not condensed so as to reflect 

 light; and "the exterior parts of the coma, or 

 tail, which have been found to be polarized in 

 a plane, showing the light to come from the 

 sun, may be supposed to consist of the vapor 

 of the nucleus, condensed into widely-scattered 

 particles of great minuteness. Mr. Huggins 

 docs not support the Tyndall theory on the 

 ground that it is inconsistent with the observed 

 appearances and forms of the tails, and espe- 

 cially with the rays frequently projected in a 

 direction different from that of the tail ; and 

 adds that, for further knowledge of the nature 

 of cometary phenomena, we must, doubtless, 

 wait until the spectrum analysis can be applied 

 to the series of changes presented by a bril- 

 liant comet. 



Prizes for the Ditcovery of Comets. The Im- 

 perial Academy of Sciences of Yienna have is- 

 sued a circular, offering prizes for the discovery 

 of comets. It says that, for several years past, 

 there have been remarkably few discoveries of 

 new comets a fact attributed to the special 

 attention given by observers to small planets. 

 The Academy regard it as very desirable, that 

 more should be known about comets, in view 

 of the recently-established connection between 

 those bodies and meteors. They, therefore, 

 propose to award a gold medal, or twenty 

 Austrian ducats, representing its value in 

 money, as the receiver may choose, for the dis- 

 covery of any new comet during the three 

 tween May 31, 1869, and May 31, 1872. 



6. Application for the prize must be made to the 



not be considered. 



7. The Imperial Academy will procure the de- 

 cision of the permanent astronomers of the Obser- 

 vatory at Vienna as to the fulfilment of the condi- 

 tions in Nos. 1, 3, and 4. 



The Radiation of Heat from the Moon. At 

 the May meeting of the Eoyal Society, the Earl 

 of B.osse presented a paper giving the fruits 

 of his experiments to estimate the amount 

 of heat which reaches the earth's surface 

 from the moon. Professor Piazzi Smith had 

 experimented for the same purpose, on the 

 Peak of Teneriffe, with a thermopile, but ap- 

 parently without any means of concentrating 

 the moon's heat beyond the ordinary polished 

 metal cone. Melloni had employed a glass 

 lens of about 3 feet diameter, but, as glass ab- 

 sorbs rays of low refrangibility, it was not so 

 well adapted to concentrate heat as a metallic 

 mirror. The point sought to be determined by 

 Lord Eosse was, in what proportions the 

 moon's heat consists of: (1.) That coming 

 from the interior of the moon which will not 

 vary with the phase. (2.) That which falls 

 from the sun on the moon's surface and is at 

 once reflected regularly and irregularly. (3.) 

 That which, falling from the sun on the moon's 

 surface, is absorbed, raises the temperature of 

 the moon, and is afterward radiated to the 

 earth as heat of low refrangibility. The ap- 

 paratus consisted of a thermopile of two ele- 

 ments, on which all the moon's heat, which 

 falls on the large speculum of the author's 3- 

 foot telescope, was concentrated by means of a 

 concave mirror of 3 inches aperture, and 2.8 

 inches focal length. Two wires were connect- 

 ed with the two poles of each pile, and the 

 ends of the wires joined two by two close to 

 a Thompson's reflecting galvanometer, in such 



