Laboratory Studies -26- 



Raymond L. Neubauer was associated with the later stages of the project 

 in the development of instruments and studies of silver -iodide smokes. 



Robert Smith- Johannsen, associated with the project during its earlier 

 history, was principally concerned with the study of the supercooling of water. 



Duncan Blanchard was temporarily associated with the project in con- 

 nection with the study of water droplets. 



Myer Geller , temporarily associated with the project, contributed im- 

 portant calculating work. 



Charles Woodman , temporarily associated with the project, contributed 

 important mathematical work. 



Arthur Parr , a Research Laboratory machinist, built almost all the 

 special equipment and developmental instruments involved. 



ICE NUCLEI 



One of the most important phenomena associated with the study of the 

 physics of clouds is the formation, distribution, and relative abundance of 

 nuclei for the formation of ice crystals. This subject, therefore, occupied 

 the attention of the principal members of the Research Group to a greater 

 or less extent throughout its history. 



Considerable work was done in developing instruments and methods 

 for detecting the presence of, and counting, such nuclei in the atmosphere. 

 Relatively early in the history of the project, a station was established by 

 Schaefer at the Mt. Washington Observatory for regular observations of the 

 concentration of such ice -forming nuclei, and these observations continued 

 over five years. Subsequently, Schaefer found in the laboratory that certain 

 kinds of soils, when dispersed as a dust, were moderately good nuclei under 

 certain atmospheric conditions. (43) 



At the time of writing this report, the number of ice nuclei needed in 

 a supercooled cloud to initiate a chain reaction (see page 28) was not yet 

 known, but evidence found early in the history of the project, suggesting 

 that a critical concentration is found in the range of 10,000 to 50,000 nuclei 

 per cubic meter, has consistently been strengthened since. (54A) 



Observations of ice nuclei were also conducted at the Research and 

 Development Division of the New Mexico School of Mines at Socorro, with 

 whom the scientists of Project Cirrus maintained a close liaison. 



