98 Chronicles of Science. [Jan., 



annoying indistinctness of objects observed near the horizon. In 

 such observations as will have to be made during the coming 

 transits of Venus, it would be of the utmost importance to get rid 

 of this indistinctness. There would then no longer be any necessity 

 for limiting the stations where observers should be sent to places 

 where the sun would have a considerable elevation above the 

 horizon. And this would be an immense advantage, because at all 

 the stations which would otherwise be the best the sun will be 

 low. Now the Astronomer Royal has shown that by means of a 

 set of flint prisms, of small refracting angle, the observer can get 

 rid in great part of the annoying dispersion we have spoken of. 

 One prism only is used at a time, the prisms of the larger re- 

 fracting angles being used for an object close to the horizon. The 

 following reports by Mr. Carpenter (of the Greenwich Observatory) 

 establish in the most satisfactory manner the value of the new 

 method. 



1869, July 15, Ilk 50m. to 12 h. 20m. Saturn, zenith- 

 distance about 82°, viewed with the great equatorial power 245. 

 Atmospheric disturbances very bad: — Prism 12° corrected the dis- 

 persion perfectly ; prism 8° corrected it fairly ; prism 6° corrected 

 it partially ; prisms of smaller angle had no effect. 



1869, July 21, 9h. The moon, zenith-distance about 78°, 

 viewed with the altazimuth, power about 100. Prism 2° slightly 

 diminished the colour; prism 4° better than the last; prism 6° 

 destroyed the colour entirely. The definition of the details about 

 the moon's ragged edge very much improved. Prisms of larger 

 angle gave an opposite dispersion. 



This plan is obviously as satisfactory as it is simple. It cannot 

 but be regarded as of extreme value and importance ; and, simple 

 as it is, will take high rank among the many important improve- 

 ments which the Astronomer Eoyal has effected in the science of 

 Observational Astronomy. 



Mr. Proctor puts forward, in a paper " On the Distribution of 

 the Nebulas," illustrated by four folio engravings, a new theory 

 respecting the constitution of the universe. He expresses his belief 

 that the nebulas are not external galaxies, but that all their varie- 

 ties are included within the sidereal system. In another paper 

 he indicates a method for measuring the discs of those stars which 

 are liable to be occulted by the moon. This method consists in 

 causing the image of a star to rotate rapidly in a circle, which is 

 itself rotated, but less swiftly. Thus the image of a star follows 

 an epicycloidal path, many coils of which will be visible simulta- 

 neously, owing to the persistence of luminous impressions. "When 

 the moon occults a star (a process which in reality occupies but a 

 small fraction of a second) the coils will vanish, but according to 

 the greater or less duration of the occultation a larger or smaller 



