1867.] 



made with a Rigid Spectroscope. 



9 



ment was placed, having observed it by far the most frequently, and 

 having given considerable attention to it. The observations were made 

 at noon daily, and, owing to the deficiency of light, have (at Mr. Brown- 

 ing's instance) been made by bringing the moveable micrometer wire 

 into the centre of the right bright space instead of its right edge, 

 as I understand was the use at Kew. 



" The diagram seemed to show that the barometer affects the instru- 

 ment, the micrometer reading increasing as the barometer falls, and 

 vice versa. In this regard it is curious that, from a series of twenty 

 observations, taken since we have been in the Straits of Magellan, 

 Mr. Connor deduced that the micrometer should read 3*84 when the 

 barometer was 30 inches and attached thermometer 54° T., and that a 

 few days since, when the barometer and thermometer were as above, the 

 micrometer reading was 3 "86. The fluctuations shown when the ship 

 was stationary seemed to poiat out that at least the barometer has 

 very considerable effect upon the reading of the instrument: what 

 amount of the general changes shown may be due to change in the 

 coefficient of terrestrial gravity I leave to those who have made the 

 spectrum their study to determine. 



" The barometer readings shown on the diagram have purposely not 

 been reduced to the mean temperature of 32° Fahr., as it is thought they 

 show better what is desired than if they were so ; should it be thought 

 advisable to reduce them it can easily be done, as the temperature of 

 the air-thermometer plotted hardly differs perceptibly from that 

 attached to the barometer. The observations are still being made 

 daily, and the record of them kept ; if any change of position, other 

 method of observing, or any other alteration is thought advisable by 

 those interested in the observations, it shall receive all the attention 

 the nature of the service on which we are employed will permit us to 

 bestow. 



" I have the honour to be. Sir, your obedient Servant, 



(Signed) " E. C. Matne, Captain." 

 " Captain Bichards, R.JSF., HydrograpTier, Admiralty.'^ 



As the diagrams referred to could not be conveniently engraved for 

 insertion in the Proceedings, they remain at the Eoyal Society. 



The observations of Captain Mayne and Mr. Connor have evidently 

 been made with great care ; the diagrams executed by the latter gen- 

 tleman exhibit at a glance the actual results. 



In these diagrams two series of observations are recorded ; the first 

 exhibits the spectroscope reading, along with the reading of the baro- 

 meter, of the thermometer imbedded in the glass prism, and of that 

 showing the temperature of the air around the instrument as the vessel 

 proceeded on its course. 



The second exhibits similar records, made when the vessel stopped 



