ON DETERMINATION OF GRAVITY AT SEA. 51 



is one of the many researches which have suffered on account of the 

 favourable conditions as attended their conduct on the Ascanius. This 

 is one of tlie many researches wliich liave suffered on account of the 

 war. 



In addition to the main Hne of attack it was considered of interest to 

 repeat a method wliich had been used in 1866, when the readings of mer- 

 cui-ial and aneroid barometers were compared. Mr. Whipple, of the 

 Meteorological Office, has described the aneroid which the Cambridge 

 Scientific Instrument Co. kindly lent the experimenter for this occasion 

 (vide ' Journal Eoyal Meteorological Society ') and the Meteorological 

 Office kindly lent a dial mercurial instrument. A criticism of this 

 method will appear in the main Eeport. Messrs. Cossor constructed to 

 the design of the Secretary a third piece of apparatus in which, as in 

 Hecker's method, a column of mercury was balanced by the pressure 

 of air in a reservoir, but it was arranged that the volume of air could be 

 kept constant by introducing into or removing from the vertical column 

 a quantity of mercury whose volume could be measured. In spite of the 

 efforts of the Secretary and of Dr. Sadler, whose assistance in installing 

 the apparatus in the refrigerator laboratory is very gratefully recorded, 

 it was not found possible to get this last piece of apparatus into working 

 order before the ship sailed; during the voyage this was accomplished, 

 but the working loose of a glass tap, though bound with an india-rubber 

 band, let air into it, causing the glass to break. Experimenters with 

 glass apparatus may be warned that on hoard ship the constant vibra- 

 tion imposes conditions foreign to those pertaining to their laboratories 

 ashore. Through the courtesy of Professor Kerr Grant, of the Adelaide 

 University, the workshop of the Physical Laboratory of that institution 

 was placed at the disposal of the Secretary for the repair of the 

 apparatus, but in spite of the efforts of Mr. Eogers, the head of the 

 workshop department, whose skill as a glassblower enabled him to 

 reconstruct the apparatus, it was not found possible to get it adjusted 

 before the time came to re-embark upon the homeward voyage. 



In conclusion, it is to be feared that results capable of determining 

 the fluctuations of gravity over a large surface of the globe have not 

 been obtained. The most that can be hoped for is that local variations, 

 such as obtain when one passes from deep water into a shallow 

 harbour, may have been at favourable times determined. It cannot, 

 however, be doubted that the experience gained of the different kinds 

 of apparatus, and of the various errors to which they are liable, will be 

 of service in some attack upon the problem which it is hoped that the 

 Committee will undertake in the near future. 



p. 2 



