406 smith: volcanic ash 



This setting can be made with a precision fully equal to that of 

 the Gauss ocular under the most favorable conditions. When 

 the plane surface to be set upon is but a few square millimeters 

 and the Gauss ocular cannot be used at all, the new form gives 

 excellent results. 



The new ocular is used for photometry by simply rotating the 

 reflecting prism 180° so that it faces toward the eye instead of 

 the objective. Uniform illumination is secured by placing a 

 fragment of opal glass over the outer end where the light enters. 

 This arrangement has been used considerably at the Bureau of 

 Standards in the measurement of diffuse reflection and transmis- 

 sion but it has not yet been tried on extra focal star images. 



This thin form of reflecting prism has been used with great 

 success in microscopes for illuminating the object viewed. It has 

 the advantage over other forms of illumination of interfering but 

 slightly with the visual beam and resolving power of the instru- 

 ment. 



The form of ocular described above was devised and used by the 

 author at the Bureau of Standards about two years ago. It has 

 proven so serviceable that it was thought advisable to publish a 

 description of it. 



GEOLOGY. — Fall of volcanic ash on Seward Peninsula, Alaska, 

 in 1907. Philip S. Smith. 



The renewed interest in volcanic phenomena caused by the 

 recent eruptions in southwestern Alaska warrants a statement 

 concerning a fall of volcanic ash in Seward Peninsula in 1907, 

 that has hitherto been unrecorded in scientific journals. 



The ash is reported to have begun falling at Nome in the eve- 

 ning of November 24 and to have continued until the morning of 

 November 28. The ash was reported from all parts of Seward 

 Peninsula and even from places as far east as the Yukon. Samples 

 were collected and have been preserved by the Geological Survey 

 from the following localities : Nome, Solomon, Teller, Alder Creek 

 in the Bluestone Basin, Lost River, York, Kingegan, Cheenik, 

 Candle, Nulato, and Unalakleet. All of the material is dark 



