GEOPHYSICAL LABORATORY. 135 



of its crater with the intrepid director of the Vesuvius observatory, 

 Professor A. Malladra, securing valuable specimens of ejecta, observa- 

 tions of temperature, and nearby photographs of the activity now 

 prevailing there. In the laboratory Mr. Perret has also developed a 

 remarkably compact microphone system and recorder for studying 

 the subterranean sounds of volcanoes with the ultimate purpose of 

 correlating these with consequent smiace phenomena, if it shall prove 

 practicable to do so, and thus to permit the accurate prediction of 

 eruptions. Of course a systematic study such as will be necessary 

 before confident predictions can be made must cover a considerable 

 time, but a vast saving of human life may result from it if successful. 

 Mr. Perret's report of the work of the year wall be found on a later page. 



The third matter which marks the present year for special distinction 

 in the history of this laboratory is a direct consequence of the European 

 war. Since April last the staff' and resources of the laboratory have 

 been concentrated in large degree upon the vital problem of producing 

 within the United States, from American materials, both a quality 

 and a quantity of optical glass adequate for national needs. At the 

 time of the entrance of the Geophysical Laboratory into this field of 

 activity the quality of optical glass available was admittedly unsatis- 

 factory; it contained striations indicating an absence of homogeneity, 

 "stones" (undissolved fragments of the pot or the glass charge) were 

 frequent, and the waste in cutting out pieces suitable for optical instru- 

 ments was very great. Moreover, the transparency of all the American 

 glasses was altogether inferior to that of foreign make regularly used 

 before the war because of impurities in American raw materials which 

 had not at that time been identified. 



In confronting this situation the Geophysical Laboratory was obhged 

 to take into account a dominant factor not directly connected with the 

 art of glass-maldng, namely, the inmiediate need for a quantity of 

 glass at least tenfold greater than normal requirements. Obviously, 

 therefore, there was no time at the moment for a thorough investigation 

 of details thi'ough which the quality of the glass could be greatlj^ im- 

 proved. The problem was rather to scour the countr}- for the best 

 raw materials available in adequate quantity and to concentrate effort 

 to manufacture these materials ill the shortest possible time into toler- 

 able glasses of the various types considered imperatively necessarj\ 

 This was accordingly the course pursued. 



Of the difficulties and details developed by the problem, it is not 

 possible to give an adequate account in a report of this kind. Suffice 

 it to say that with a group of 20 scientifically trained men, all skilled 

 in handhng silicate solutions at the temperatures required for making 

 glass, and familiar v/ith the control of most of the factors in the prob- 

 lem, it proved practicable to make rapid progress and in June following, 

 after two months of concentrated effort, the gross production of glass 



