26 REPORT OF THE SECRETARY, 



and this almost intinitesimal amount is disting-uishod with readiness 

 and precision. It is this increased precision which is associated with 

 all the improvements in the work of the year here described. 



It is the variability of the absorption of our air which now offers 

 the greatest difficulty to the work. The Secretary cherishes the hope 

 that a solar observatory will one day be established high in a clear and 

 dry air, whose chief aim shall be to solve the questions of the amount 

 of radiation of the sun, the changes in this total amount, and the con- 

 sequences of such changes on the earth. 



The interest of this solar stud}^ is peculiar among all the subjects of 

 astronomical research, for it is not only a scientific but a utilitarian 

 interest of such high importance that it has among its remote possibili- 

 ties the forecasting of the coming seasons and harvests, and of conditions 

 immediately practical, from those which affect the price of the laborer's 

 dinner up to those which, to use the weight}' words of Professor New- 

 comb, may bring to light not merely interesting cosmical processes, but 

 "cosmical processes pregnant with the destiny of our race,"" 



In connection with these researches it has proved necessary to 

 obtain a large solar image as free as possible from defects of definition 

 and unequal absorption. One of the most formidable of these defects 

 is that which astronomers call " boiling.'" This consists of an apparent 

 wavy and rolling motion over the image, and is due to momentary 

 differences of density of the air in the path of the beam. It has 

 hitherto been sought (with little effect) to control this by keeping the 

 air in the tube as still as possible. 



I am nmch interested in a new plan which I have myself proposed, 

 that of thoroughly and incessantly stirring this air column even while 

 the rays forming the telescopic image are passing through it. This 

 experiment of stirring the air has been tried during the past few 

 months at the Observatory, and has resulted in the discovery that by 

 vigorously churning the column of air traversed by the solar beam 

 from a point about 50 feet above the apparatus to the point where the 

 image is formed, the paradoxical result is reached that this image itself 

 becomes nearly tran(|uil, and that thus the "boiling" can be nearly 

 all eliminated. It is hoped that this very important observation will 

 prove useful to astronomers generally. 



For details of the work of the Observatory, including many inter- 

 esting su])jects in addition to those I have mentioned, the reader is 

 referred to the rejMirt of the aid acting in charge, which appears in 

 the Appendix. 



NECROLOGY. 



The Institution litis lost by death its presiding officer, ex officio, 

 William McKiidey, President of the United States. The life and 

 work of that honored and emiiu'iit man and the tragic circumstances 

 of his death are in all minds and they need not i)e repeated here. 



