MOUNT WILSON OBSERVATORY. 211 



Professor Michelson's work as a Research Associate of the Obser- 

 vatory will be continued and extended in various directions. In addi- 

 tion to his investigations on the astronomical applications of the inter- 

 ferometer, he has undertaken a new determination of the velocity of 

 light by an improved method, which promises results of the highest 

 accuracy. Preliminary tests made this summer over a distance of 

 about 4 miles were so satisfactory that a range of 16 miles is now 

 being tried, and it is hoped that it may prove feasible to use in the final 

 work a still greater distance between stations (p. 253). 



The area of the 100-inch mirror is about 2.8 times that of the 60-inch, 

 and the Hooker telescope, under perfect atmospheric conditions, should 

 theoretically reach stars about a magnitude fainter than we have been 

 able to observe with the smaller instrument. This advantage has 

 been fully attained in spectrographic observations under good condi- 

 tions, thus permitting an important extension of our investigations of 

 stellar spectra (p. 245). To show that an equal gain can be secured 

 in direct photography, a series of comparative photometric tests has 

 been nia,de. These indicate that mth seeing 6 on a scale of 10, stars 

 nine-tenths of a magnitude fainter than those reached by the 60-inch 

 can be photographed with the Hooker telescope during the same 

 exposure- time. Moreover, the details of the moon's surface and the 

 minute structure of nebulae are much better shown with the larger 

 instrument. Thus the most exacting and rigorous comparative tests, 

 made simultaneously under identical atmospheric conditions, using 

 plates from the same box, developed in the same tray, prove con- 

 clusively that the Hooker telescope has met our highest expectations. 

 (p. 230). 



The increased light-gathering power of the new instrument should 

 add several hundreds of millions of stars to those already known. For 

 certain classes of work, a further advantage can be attained by means 

 of a simple device due to Mr. Shapley, who mounts a converging lens 

 system a short distance in front of the photographic plate, thus con- 

 centrating the starlight in a smaller ''tremor-disk" through a virtual 

 reduction in the focal length of the telescope. The gain in light-gather- 

 ing power over the 60-inch telescope used without this device is more 

 than two magnitudes. While the field is necessarily limited through 

 the interposition of the lens, this method has already proved its value 

 in the investigation of star-clusters and nebulae (p. 243). Another 

 useful device for the study of the faint stars in crowded clusters is a 

 large prism, mounted before the plate at the 134-foot Cassegrain 

 focus (p. 242). 



In this connection mention should be made of the visit of Professor 

 Wright, who brought his sUtless quartz spectrograph from the Lick 

 Observatory in June in order to try it at the Newtonian focus of the 



