NUCLEATIONS ACCORDING TO BARUS. 
BY L. BEGEMAN. 
No doubt all students of science have read more or less about Barus’ 
work on condensation phenomena as produced in a specially constructed fog 
chamber. As is known, his work has been done under the direction of the 
Carnegie Institution of Washington, founded particularly for the solution of re- 
search problems, involving much time and considerable expense. The prime 
purpose of his work, so far as I can interpret it, is to determine the part 
played by various kinds of nuclei in the atmospheric condensation of vapor. 
This, of course, is a very interesting problem to the student of physiography, as 
well as to the physicist. 
It is very difficult to read Barus’ notes and I would not commend his style to 
anyone. In fact, I doubt whether anyone who has not had some experience 
in the experimental production of such phenomena could get much out of his 
writings. His literature is apparently intended for the few who have the cour- 
age to attack something exceedingly dry. In my experimental work to deter- 
mine the charge of an electron I had occasion to refer to his work to help 
interpret my own phenomena. In the discussion of my work I have made fre- 
quent reference to Barus and it is for this reason that I present this sketch 
with the hope that it will make the other paper more intelligible. 
Barus’ fog chamber is sketched in a simple manner without detail in Pig. 1. 
It consisted of a cylindrical vessel made either of glass or wood and sealed air 
tight. The lower part of the vessel contained a layer of pure water which kept 
the air or gas above in a state of supersaturation. The vessel contained also a 
number of wet muslin partitions placed parallel to its length. The purpose of 
these was to prevent cross currents in the vessel when the exhaustions were 
made, thus keeping the clouds uniformly compact. The tube E leads to a 
vacuum chamber cut off by an intervening plug valve. By the sudden opening 
of the plug valve an exhaustion of the fog chamber is made, producing a conse- 
quent lowering of temperature which results under the proper conditions when 
nuclei are present in the formation of a cloud. A bright beam of light is ad- 
mitted into the fog chambers so that when a cloud is produced a coronna, gener- 
ally of a green-blue-purple type, is plainly visible. The angular diameter of 
the coronna is measured by a pair of goniometers suitably placed and from this 
the number of efficient nuclei are determined in a manner described in Barus’ 
publication of the Smithsonian Institute, published in 1905. 
Barus describes three kinds of nuclei which at given pressures are able to 
induce the condensation of vapor in a fog chamber by exhaustion. First, “the 
ordinary dust-like persistent nuclei which require the smallest degree of super- 
saturation to induce condensation. Ordinary air, particularly of cities, contains 
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