May 15, 1908] 



SCIENCE 



793 



of the inner mountainous island; the lower 

 wooded slopes; and, dominating all, the cen- 

 tral, gray-white peak. 



WORK OF THE COAST AND GEODETIC 

 SURVEY 



The report itseK must be consulted for the 

 details of the extensive cartographic work of 

 the Bureau in the United States proper, 

 Alaska, Porto Kico and the Philippines, as 

 well as for the account of the progress of the 

 primary triangulation and leveling of pre- 

 cision. In all these branches of the work 

 great activity prevailed and notable results 

 were achieved during the year. 



Certain important work of the survey re- 

 ceives bare mention, as for instance the results 

 of the investigation of the earth's figure 

 based on geodetic operations in the United 

 States. This is owing to the fact that these 

 results were communicated to the Inter- 

 national Geodetic Association in a prelimi- 

 nary report which has been published. 



Appendix 1 gives the details of field opera- 

 tions, and Appendix 2, the details of office 

 work. Pive other appendixes form valuable 

 discussions of interesting subjects. 



Soon after the California earthquake of 

 April 18, 1906, it became evident that the 

 permanent horizontal displacements of large 

 areas covered by triangulation in California 

 had so changed the lengths and directions of 

 the lines joining the triangulation stations 

 as greatly to diminish the value of the tri- 

 angulation for its primary purposes as a 

 framework for future surveys. During the 

 year, therefore, new triangulation extending 

 from Point Arena to stations south of Mon- 

 terey Bay was done, which serves to restore 

 the value of the old triangulation by de- 

 termining the new positions of 61 of the old 

 triangulation stations. The triangulation in- 

 cluded the Parallen Light House, 22 miles to 

 the westward of the great fault accompanying 

 the earthquake, and the stations Mocho and 

 Mount Diablo, 33 miles to the eastward of 

 the fault. The new triangulation serves to 

 trace the permanent distortions and displace- 

 ments of the earth's crust for many miles 



back from the fault in each direction and 

 to show that they follow certain regular laws. 

 This is the most extensive and accurate de- 

 termination by triangulation of the effects of 

 an earthquake which has yet been made any- 

 where in the world. Appendix 3 is a full 

 report upon this investigation. 



A full report on the measurement of six 

 primary bases with steel and invar tapes in 

 1906 is printed as Appendix 4. The invar 

 (nickel steel) tapes have a coefficient of ex- 

 pansion about one twenty-eighth that of steel 

 tapes, hence it is much less difficult to keep 

 the temperature errors within the required 

 limit with invar tapes than with steel tapes. 

 Invar tapes had not been used in the United 

 States until 1906 in primary base measure- 

 ments. The thorough tests of these tapes, 

 made by using them on six bases in conjunc- 

 tion with the steel tapes formerly used, 

 showed that measurements may be made more 

 conveniently, accurately, and at smaller cost 

 per mile than with the steel tapes, and that 

 the invar tapes are sufficiently durable and 

 stable for safe field use. This demonstration 

 is believed to be a distinct step in advance in 

 base measurement. 



The steady progress in the magnetic survey 

 of the United States and accumulation of 

 magnetic observational data, as mentioned in 

 Appendix 5 of the report, should be of special 

 interest to the surveyor and the navigator, as 

 well as to those pursuing the study of the 

 science of terrestrial magnetism. Through- 

 out the year the measurements of the earth's 

 magnetism were made at places distributed 

 over a majority of the states and territories of 

 the United States and at numerous places at 

 sea along the Atlantic and Pacific coasts of 

 North and South America, and in Porto 

 Rico and the Philippines. Important in- 

 formation was secured in the equatorial 

 regions. Numerous " repeat " observations 

 were made throughout the country in order 

 to follow as closely as possible the secular 

 change in the magnetic elements. Five mag- 

 netic observatories were maintained in con- 

 tinuous operation and important seismological 

 data were also obtained. The facilities of the 



