434 



METEOROLOGICAL INSTRUMENTS. 



METEOROLOGICAL INSTRUMENTS. 



[Mr. Cassella, of London, has furnished us with a series of wood cuts to illustrate some 



late forms of instruments constructed by himself; and, as they may be interesting to 



meteorological observers, we have concluded to insert them in this Appendix to the 



Annual Report. — J. H ] 



Fig. l. 



Fig. 1 represents a solar radiation thermometer, with blackened 

 bulb, in a stout glass tube exhausted of air within one-tenth of an 

 inch of the mercurial gauge, constructed agreeably to the suggestion 

 of Sir John Herschel. 



The instrument being thus protected from all external influences, 

 gives uniformity of readings for comparison of solar radiation, which sur- 

 passes those obtained by the naked bulb exposed to contact with the air. 



Fig. 2. 



)F PHILLIPS'S 



MAXIMUM THERMOMETER 



1 I ' I ' I ' I : I ' I ' I ' | 

 CASELL'A. FECIT LONDON. 



504 



Fig. 2 represents a maximum thermometer constructed on the 

 principle of Professor Phillips. The maximum point of temperature 

 attained during the interval between two observations is indicated 

 by a separation in the mercurial column. The end of a portion of 

 the extremity of the column is left at the point of maximum, while 

 the contraction takes place in the remainder of the column, as shown 

 in the figure. To insure this separation, the bore of the tube is 

 exceedingly fine, and a minute portion of air is left by the maker at 

 the point where the separation takes place. This instrument is sus- 

 pended horizontally on a hook at one end and on a pin at the other. 

 In order to bring back the index to its proper place after the obser- 

 vation has been made, the pin is removed, the instrument is brought 

 to a perpendicular position with the bulb downwards, when the 

 detached mercury descends into near contact with the remaining 



