F. GEOGRAPHY. 251 



system when a large area is to be covered ; a series of quad- 

 rilaterals is the system possessing the greatest strength or 

 accuracy. The relative values of these three systems may be 

 determined by the consideration that the first, or triangular, 

 requires the least number of stations ; the third, or quadrilat- 

 eral, necessitates the shortest lines of sight, and therefore 

 the least obstruction by fog, haze, woods, etc. Among aux- 

 iliary methods which are needed for short distances where 

 ordinary triangulation can not be applied, if we do not resort 

 to actual measurements of long lines with rods or wires or 

 rolling-wheels, w T e adopt that of Struve, which consists in 

 measuring a number of small base-lines at right angles to 

 the main course of the triangulation, so as to have one within 

 each of a series of elongated quadrilaterals. Appendix XV ., 

 Coast Survey Report, 1871. 



THE MEAN HEIGHT OF EUEOPE ABOVE THE SEA LEVEL. 



The mean height of Europe above the sea level has been 

 recently determined by Leipoldt, who calculates that it is 

 about equal to 297 meters, which is 92 meters higher than 

 the calculation of Humboldt. The mean height of Great 

 Britain is 218 meters, and of Switzerland 1300. 



GEODESY IX SWITZERLAND. 



From the report of the Natural History Society of Switzer- 

 land we gather that the publication of the three sections of 

 the primary triangulation work is now nearly completed. 

 During the past year experiments with Bessel's reversion 

 pendulum have been carried out by Plantamour, and exact 

 levelings made, in order to connect together the principal 

 stations. These latter have been investigated by Redard, 

 who has found an error in altitude of one meter in the earlier 

 portion of the work, between Locarno and Domodossola, by 

 the rectification of which there seems now reasonable cer- 

 tainty that the entire Alpine polygon will exhibit no sensible 

 error. Ver. Schweiz. Katur. GeselL, 1874, 113. 



TRIGONOMETRICAL SURVEY OF INDIA. 



According to the annual report of the Indian Trigonomet- 

 rical Survey, seventy principal triangles, embracing an area 

 of 7200 square miles, and extending over a linear distance 



