500 Scientific Intelligence. 



screen. It was found that there was, as expected, an abrupt 

 limit of distance in the power of the positive rays to produce 

 phosphorescence. — Phil. Mag., Nov. 1907, pp. 614-61*7. j. t. 



9. The Vacuum Bolometer. — It has often been observed that 

 a bolometer strip placed in a vacuum is more sensitive than in air. 

 E. Warburg, G. Leithauser and Ed. Johansen have investi- 

 gated this phenomenon and give a tabulated resume of their 

 results. The conditions of sensitiveness vary with the strength 

 of currents employed and the breadth of the bolometer strips ; in 

 general the sensitiveness in a vacuum is from three to four times 

 that in air. — Ann. der Physik, No. 11, 1907, pp. 25-42. j. t. 



10. Ratio of the Electrical Units. — The paper by E. B. Rosa 

 and N. E. Dorset on a new determination of the ratio of the 

 electromagnetic to the electrostatic unit of electricity, alluded to 

 in the last number (p. 442), is completed in the current issue of 

 the Bulletin of the Bureau of Standards (pp. 541-604). The 

 final value obtained reduced to vacuo (assuming the dielectric 

 constant of air at 20°C and 760 mm as 1-00055) is 



V = 2-9971X10 10 



Accepting the velocitj'' of light as 2*9986 X10 10 , this value of v a 

 shows a difference of 5 parts in 10,000 with a possible uncertainty 

 of 2 parts in 10,000. The explanation of the resulting difference 

 (1 in 3000) is as yet uncertain. A supplementary paper by the 

 same authors (pp. 605-622) gives a critical comparison of the 

 various methods of determining the above ratio. 



II. Geology and Mineralogy. 



1. The Geology of Worth Central Wisconsin ; by Samuel Weid- 

 man. Wisconsin Geol. and Nat. Hist. Surv., Bull. xvi. Madison, 

 1907, Svo, pp. 697, maps in cover. — The area whose geology is 

 described in this memoir contains about 7200 square miles, about 

 one-eighth of the state, and is situated as described in the title. 

 The city of Wausau (15,000 pop.) near the center is the largest 

 place in the district. It is without especially characteristic topo- 

 graphic features and is chiefly an agricultural country. 



The geological problems of the district are mainly those relating 

 to the pre-Cambrian rocks, which consist to a relatively small ex- 

 tent of metamorphosed sedimentaries and very largely of igneous 

 intrusives, and those relating to the latest deposits, which are Pleis- 

 tocene, or glacial. One-half of the volume is, therefore, devoted 

 to the working out of the petrographical problems presented, the 

 other to glacial geology and pl^siography. In the time-interval 

 between these two, the Paleozoic alone is represented by the Pots- 

 dam sandstone. Of the igneous rocks, the most interesting are 



