86 Memoir o* the late 



ment efficient by shewing at all times what the derangement 

 amounts to. Before sealing the end of the bulb a a, I propose 

 to insert a delicate mercurial thermometer on an ivory scale 

 g g g similar to the one inserted in the bulb and stem of 

 Daniel's hygrometer. The reading of this inside thermome- 

 ter will be a check on the error arising from the transfer of 

 alcohol from side to side of the syphon, and when the regis- 

 ter differs from the inside mercurial thermometer reading the 

 difference must be used to correct the register. With a 

 Sikes' thermometer thus constructed and placed in the open 

 air. it will soon be seen how variable the differences between 

 the register and the enclosed thermometer are, in conse- 

 quence of the alcohol passing from side to side of the syphon 

 to restore the equilibrium. Indoors, where the range of 

 temperature is small, the differences will be much less. 



In concluding, it may be well to mention another source of 

 variation between the readings of a mercurial and of a spirit 

 thermometer, which for registers requires to be guarded 

 against. It is the action of light on the opaque mercury and 

 the transparent alcohol : the light increases the temperature 

 of the opaque body more than that of the transparent one ; 

 consequently in a bright day, a mercurial thermometer gives 

 a higher reading than one of alcohol does, and to obtain from 

 them corresponding results the light must be excluded. On 

 the mercury thermometer in the bulb of Sikes' thermometer 

 the effect of the light will be nearly prevented by the alcohol 

 in contact with the mercurial bulb ; so that in this proposed 

 construction, in a bright light the mercury and spirit will 

 read closely together, both standing lower than a detached 

 mercurial thermometer. 



Memoir of the late Dr Thomas Thomson, F.R.S., M.W.S., 

 fyc., Professor of Chemistry in the College of Glasgow. 

 Communicated by his relative, Dr R. Dundas Thomson. 



[Having laid before our readers Gustav Rose's complete 

 biography of Professor Berzelius, it is now our duty to com- 



