Masterpieces of Science 



searched for, especially in the tufa of volcanoes, 

 but thus far without assured results. 



Toward the end of the spectrum, beyond the 

 red, are invisible radiations which evaded capture 

 until 1887, when Captain Abney secured an image 

 from them on a bromide-of-silver plate. He main- 

 tains that in the use of plates sensitive to such 

 ultra- visible rays, astronomers have a new means 

 of exploring the heavens, and are free to enter 

 upon a fresh chain of discoveries. To the stars 

 already known it is in their power to add two 

 classes as yet unseen stars newly born or newly 

 dead, whose temperatures in consequence are 

 below the range of visible incandescence. 



When light succeeded the pencil as a limner of 

 nebulae there was the keen interest that attaches 

 to the calling of a new witness in a case before the 

 highest court a witness so much more observant 

 and alert than any other, so absolutely devoid of 

 bias or prejudice, that his evidence decides the 

 verdict. For a century and more the nebular 

 hypothesis of the universe, propounded by Kant 

 and Laplace, had been vigorously debated by 

 astronomers and physicists. The great tele- 

 scopes of the two Herschels had enabled ob- 

 servers to descry nebulae having the shapes which 

 vast cloudy masses would assume in the succes- 

 sive phases of condensation imagined in the 

 theory. Some were spherical in form, others 

 were disc-like, yet others were ring-shaped, and 

 the most significant outline of all, that of a spira, 

 was also discerned. But when Lord Rosse's 



