CHAPTER IX. 



THE NUCLEATION OF THE ATMOSPHERE OF THE CITY OF PROVIDENCE. 



INTRODUCTION. 



1. Prcliniinary. — In May, 1902, Mr. Harvey Davis, at my request, put 

 up an apparattis in the laboratory of Brown University for counting the number 

 of nuclei in the atmosphere, by measuring the coronas producible with such air 

 under appropriate conditions. The apparatus gave promise at once; but Mr. 

 Davis was unexpectedly called away before the observations became fruitful, 

 and the project was temporarily abandoned. Believing that an instantaneous 

 method of at least estimating the degree of atmospheric nucleation is a de- 

 sideratum, and must throw light eventually on the origin and character of the 

 nuclei in the atmosphere, I have tmdertaken the furtherance of the work my- 

 self, and the results obtained since October, 1902, after the indications of the 

 apparatus had become warrantable, are given in the present chapter. I may 

 add that Mr. Davis and Mr. R. Pierce, Jr., had been at work for some time on 

 the measurement of the daily variation of the solar constant (a project then 

 set on foot by the U. S. Weather Bureau), and that I had hoped from the co- 

 ordination of the two classes of data to reach conclusions of interest. 



The chapter, therefore, contains nearly two years of continuous record of 

 the nucleation of Providence, R. I. The observations were made in the park 

 of Brown University, which is surrounded, however, on all sides by the city. 

 The density of population lies to the west and so^ithwest. A station entirely 

 away from the habitations of man would naturally have been preferable, but 

 this desideratum was at the outset out of the question. 



2. Apparahis. — The apparatus and method by which the present results 

 were obtained are fully given in the chapters above, particularly in Chapter VIII, 

 and need not therefore be further considered here. In figure i, however, I have 

 shown a simplified train of apparatus used in some of my early work (October 2 , 

 1902, to March 15, 1903). Here J is the influx tube, Z> the water-bath at room 

 temperature, t the thermometer, A the condensation chamber (the water w is 

 made to wet the sides by rotating A before expansion) , R the vacuum chamber, 

 G the gauge, 5 the pipe to the suction pump. Stopcocks h and c control the 

 exhaustion, together with a. 



3. Classification of results. — The results themselves may be embraced in 

 two groups. The first group of observations, from October 2, 1902, to March 



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