Scientific Lectures. 279 



might suppose that the granules are recently condensed incandescent 

 clouds ; that they slowly sink, merge into each other, become less and 

 less luminous, and gradually dissipate into comj)aratively non-lumin- 

 ous gas. The dark pores would then be represented by the portions 

 where complete vaporization had taken place." He also gives an. 

 interesting diagram, which is here reproduced in a drawing by Prof. 

 Morton, to show the distribution of the bright granules on those 

 parts of the sun which are free from spots, in some of the most char- 

 acteristic forms of their grouping. Thus it seems established that 

 the luminous surface of the sun is entirely composed of these glowing 

 particles or granules, almost as small as we can see, notwithstanding 

 that they can scarcely be less than TOO miles in length, floating in a 

 sea of darker though luminous fluid matter. The brighter and the 

 darker mottlings of the ordinary surface, the brilliant glow of the 

 fjicula3, and the dimmed lustre of the penumbra, must alike be refer- 

 red to the intrinsic splendor of individual granules, distributed in 

 various ways, arranged more or less compactly and at difterent degrees 

 of submergence in the fluid medium Avhich supports them. Lockyer, 

 a young English astronomer, who has done much to advance our 

 knowledge of the constitution of the sun, says that he has seen the 

 granules in the penumbra change their axial directions, and others, 

 visible against the nucleus as a background, gradually to melt away. 

 Chacomac says, moreover, that the granules, or crystals as he calls 

 them, may be seen dissolving away like crystals of sugar before a jet 

 of steam, becoming spotted over with dark points before they finally 

 disappear. 



Diminution of the Sun's Force. 

 The great fact, to which I have more than once alluded, that the 

 sun is practically our only source of earthly power and energy, gives 

 a peculiar interest to the question whether his brilliancy or thermal 

 energy are undergoing any perceptible diminution. That they are 

 diminishing we must assume on general principles, inasmuch as we 

 know to what an inconceivable extent he is radiating force in the 

 various forms of heat, light and chemical power, and force once 

 emitted from a source of such superior energy is not returned to it 

 again, while a new creation of force by natural agencies is just as 

 impossible as a new creation of matter. But whether any diminu- 

 tion of radiant energy in consequence of the enormous expenditure 

 is perceptible by our means of investigation is a most natural and. 

 important question, and to this it must be answered that no appreci- 



