APPENDIX D LXXXIX 



netic survey of the earth, undertaken by the Carnegie Institution of 

 Washington. 



Gravity. — The Observatory is provided with a half-seconds pen- 

 dulum apparatus — type Mendenhall. There are three pendulums besides 

 a " dummy '" of the same mass as the others, which is used for the de- 

 termination of the temperature of the swinging pendulum, by having a 

 thermometer intimately attached to it. The pendulums are swung suc- 

 cessively under constant pressure (GO mm.) in an air-tight chamber for 

 nearly eight hours in each of the two positions on the agate knife-edge. 

 For noting coincidences a sidereal chronometer with electrical attach- 

 ment is used. Astronomical observations of a high degree of accuracy 

 are necessary in order to determine the chronometer rate upon which 

 depend the deduced periods of the pendulums. The periods axe expressed 

 to the seventh place of decimals, i. e.. to the ten-millionth of a second 

 of time, as it is found that good observations with the same pendulum 

 will agree within the units of the seventh place of decimals. One com- 

 plete set of pendulum observations takes at least forty-eight hours, and 

 at important stations two sets are taken. Observations with a half-se- 

 conds pendulum give relative gravity, as compared with similar obser- 

 vations at a base station. With the above apparatus observations were 

 made at Washington and Ottawa, and as the former is connected with 

 the principal European base stations, observations hereafter made, will 

 be correlated to the International Gravity series. Stations occupied so 

 far are: — Washington; Ottawa; Montreal; Toronto; Northwest Eiver ; 

 Suva, Fiji; and Doubtless Bay, New Zealand. 



It is intended to carry across Canada from the Atlantic to the 

 Pacific, a chain of gravity stations, which will cover an arc of longi- 

 tude of 64°. 



Miscellaneous. 



The photographic division has been kept busy during the past year, 

 principally in the developing of the negatives taken, and the making of 

 the prints used in connection with the various surveys. A two-fold en- 

 largement is made from each of these negatives, and these are used in 

 making accurate maps of the region under survey. Moreover, copies 

 of maps and plans are frequently required, and also of the various draw- 

 ings and curves used in the astro physical division. 



The workshop has proved a most useful and indeed indispensable 

 adjunct to the Observatory. The mechanician has not been able to 

 keep pace with the work required, and an assistant has lately been ap- 

 pointed. The work of the Observatory and the allied surveys has grown 

 80 rapidly, that the repairs and alterations required are sufficient to 



