8 



Mr. J. P. Gassiot on Observations [June 20, 



them occasionally as a check, and also during the time he was laid up 

 with a wound which these wretched Euegians gave him. Ton will see 

 the method pursued in the diagram is to give the whole voyage com- 

 plete, and also the fluctuations during our stay at the various places 

 named. Let me add, what I also said to the Hydrographer, that we 

 shall be happy to carry out any changes in position of the instrument, 

 or mode of observation, you may wish, so far as our other duties will 

 permit. I shall be very glad also to hear that our observations have 

 been in any way useful. The weather we have hitherto experienced 

 has been rather better than we expected, but gale, gale, gale, the wind 

 seems never tired ; if it does for a few hours forget to maintain the 

 credit it has obtained, be sure you will find a current of five or six 

 knots directly opposed to the course you wish to pursue. 



" Please remember me kindly to Mr, Stewart when you see him, and 



" Believe me yours sincerely, 



(Signed) " E. C. Matne." 



« J, P. Gassiot, Esq., F.B.Sr 



The following is a copy of the letter referred to in the preceding 

 extract : — 



(Copy.) 



"H.M. Surveying 'Ship 'Nassau,' Straits of Magellan, 

 Feb. 15, 1867. 



" Sir, — I beg to forward the followiug remarks on the rigid spectro- 

 scope which was placed on board this ship at the request of Mr. Gassiot, 

 y.P.R.S., with the view of determining whether the position of the D line 

 of the spectrum changes with the coefiicient of terrestrial gravity. Ac- 

 companying the remarks is a diagram, intended to show at a glance the 

 fluctuations which have actually occurred in the line of the spectrum 

 during our voyage from Plymouth to the Straits of Magellan, as well 

 as those of the barometer and "air" and "prism" thermometers 

 during the same period. In addition to this it has been thought advi- 

 sable to plot in the same way the fluctuations which occurred during 

 the ship's stay at the various ports of call on the voyage out indepen- 

 dently, as they cannot of course be in any way due to change of 

 gravitation. They will be seen on the lower part of the diagram, the 

 same number of observations having been plotted after our arrival in 

 the straits as were taken at Plymouth, the two places being so nearly 

 in the same latitude. 



" A description of this instrument has been given by Mr. Gassiot 

 before the Eoyal Society. Its position on board being selected by Mr. 

 Gassiot himself, in concert with Mr. Browning, it was placed, at their 

 desire, on the port side of my cabin, and its position has in no way 

 been altered since. All the observations have been made either by Mr. 

 Connor or myself: Mr. Connor, in whose special charge the instru- 



