iv PURSUIT OF KNOWLEDGE 65 



Society in 1820, called upon him one day and asked to 

 see his laboratory. " Certainly," said Wollaston, and 

 rang the bell. " John," he said to the attendant who 

 entered, " bring up my laboratory." Whereupon John 

 went out and returned in a few moments with all 

 Wollas ton's apparatus on a tea-tray. 



Prof. E. C. Pickering, director of the Harvard College 

 Observatory, says that people used to ask if the Obser- 

 vatory possessed the largest telescope in the world. 

 He would answer, " No, but we have the smallest that 

 is doing useful work." The instrument to which he 

 referred was constructed for measuring the light of the 

 bright stars ; and its object-glass was only two inches 

 in diameter. With this, during the years 1880-1882, a 

 hundred thousand measures were made of four thousand 

 stars, mainly visible to the naked eye. Similar instru- 

 ments have since been constructed with larger lenses 

 capable of bringing fainter stars into view, but through- 

 out the work for which Harvard College Observatory 

 is famous in the astronomical world, the principle has 

 been to obtain the maximum efficiency from the instru- 

 ments available. 



This plan of making the best use of whatever is at 

 hand must always be followed if scientific work is to be 

 done. While the dreamer sighs for opportunities, the 

 inquirer works with things as he finds them. Difficulties 

 to the man of science engaged in research are only pro- 

 blems to be solved ; they may hinder progress but never 

 prevent it entirely. ' The way I get over a difficulty," 

 remarked an Irishman, "is to go round it " ; and that 

 represents the frame of mind by which advance is made 

 in every branch of human activity. 



For certain scientific purposes " gratings " are required 



on which about a hundred thousand parallel lines have 

 G.D, E 



