Kirkwood.l ^^'^ [April 6, 



Entire surfiioe covered 1))- siiiall, trian<!:ular, imbricating scales, decreas- 

 ing in size towards the lateral margins ; along the anterior portion of the 

 carapace tlw scales are not visible. The paletti (one of which is pre 

 served) long and narrow, being nearly twice as long as wide, and has the 

 characteristic serrated margin, which is the principal distinguishing 

 feature in the sub-genus. Length of specimen, without terminal joint, 

 two and three-fourths inches ; greatest breadth seven-eighths of an inch. 



Position and localit3^ Found in tlie shale immediately below the Dar- 

 lington cannel coal, near Cannelton, Darlington Township, Beaver Co. 

 Pennsylvania. Horizon, Alleghany Kiver Series. 



"We are Indebted to Mr. S. F. Mansfield, of Oannellon, for this beautiful 

 specimen, and after whom we deem it proper to name the species. 



On the Reliitive Ages of the Sun and certain of the Fixed Stars. 

 By Professor Daniel Kirkwood, of Indiana University. 



(Read before the American Philosophical Society, April 6, 1877. ) 



The doctrine that the light and heat of the sun are produced by the chem- 

 ical combination of its elements was ver}' generally accepted till about the 

 middle of the nineteenth century. It has, however, been completely dis- 

 proved by the labors of Dr. Mayer and Sir "William Thomson. The quan- 

 tity of heat radiated by the sun in a given unit of time has been determined 

 with approximate accuracy. The amount produced by the combustion of 

 a given quantity of coal is also known. From these data it is easily shown 

 that if the sun were a solid globe of coal, and a sufficient supply of oxygen 

 were furnished to support its combustion, the amount of heat resulting 

 from its consumption would be less than that actually emitted within his- 

 toric times. "Take (in mass equal to the sun's mass) the most energetic 

 chemicals known to us, and in the proper proportion for giving the great- 

 est amount of heat by actual chemical combination ; and, so far as we j'et 

 know their properties, we cannot see the means of supplying tlie sun's 

 present waste for even 5,000 j'ears. "* The chemical theorj'is accordingly 

 given uji as wholly untenable. 



What then is the source of solar energy? To this interesting question, 

 in the present state of our knowledge, but one reply is possible. The great 

 law of the conservation of force — one of the most important discoveries in 

 llie history of physical science — points at once to a cause which is adequate 

 both in mode and measure. Motion maj' be transformed into heat, and 

 vice versa. The heat |)roduced by the fall of a given quantitj' of matter 

 upon the .sun from the outer limits of the solar system would be 7,000 times 

 greater than that resulting from the combu.?tion of its own weight of coal. 

 In the mechanical tiieory of solar energy, as advocated by Ilelmholtz and 



"Tail's Recent Atlvancos In Physicul Science, Lnd Kd. p. 152. 



