THE SMITHSONIAN INSTITUTION. 219 



tlie thermometer should be taken down and shaken until the alcohol 

 runs down; it should then he kept in an upright position for some 

 time to drain. If it is found difficult to shalce down tbe condensed 

 vapor, the end of the tube may be carefully and slowly heated with a 

 small lamp, or a small rod of heated iron held at a short distance, 

 keeping the bulb and lower part as cold as possible ; the alcohol by 

 vaporization will then condense at the surface of the s])irit in con- 

 nexion with the bulb. Occasionally, in cold climates, spirit-thermo- 

 meters are deranged by the air absorbed by the alcohol becoming free in 

 the bulb at a low temperature. When this occurs bring the thermo- 

 meter to as low a temperature as may be convenient ; then hold it in 

 such a position that the air-bubble comes to the juncture of the bulb 

 and tube, warm the bulb till all the air is in the tube, then by shaking 

 the thermometer, or by gentle knocking, the spirit will flow down, 

 and the air speck come to the top. 



This does not occur in spirit thermometers that are closed with a 

 vacuum, and the spirit at the time well freed from air. In this case, 

 however, the above named difficulty from vaporization takes place 

 more readily than when closed with air. These derangements of the 

 spirit thermometer are readily rectified, and only require occasional 

 examination to detect them. 



Both the maximum -and minimum thermometers may be adjusted 

 without the magnet, by raising one end sufficiently to allow the index 

 to slide down by its own weight. 



The ordinary maximum thermometer (Kutherford's) not working 

 well, even in the hands of many careful observers, has occasioned 

 several attempts to make one without an index. 



Mr. Green has lately contrived one. The object is effected by en- 

 closing in the bulb a glass valve, which is floated by the mercury to 

 the juncture of the bulb and tube. On an increase of heat the mer- 

 cury from the bulb passes this valve, but on contraction from a de- 

 creasing temperature, the portion in the column is obstructed, and 

 remains stationary, indicating the maximum point attained. 



To set the instrument for another observation, it is held bulb down- 

 wards, and with a gentle jerk the mercury falls and joins that in the 

 bulb ; it is then placed horizontal in the usual way. 



A movable valve-piece is introduced rather than a fixed obstruc- 

 tion or stricture, as in a new and ingenious maximum thermometer 

 by Messrs. Negretti and Zambra, of London, in expectation that the 

 observer will find greater ease and satisfaction in readjusting the in- 

 strument for observation. 



Professor Pliillips, of England, has also devised one. His plan is 

 to cut off a portion of the column of mercury by an intervening small 

 bubble of air. An increase of heat drives this detached portion for- 

 ward, and leaves it there on a decrease of heat. 



This form is also made by Mr. Green, and possesses some advan- 

 tages peculiar to it ; but, until experience decide otherwise, we doubt 

 if it can be put in order after accidental derangement, by every ob- 

 server. The former plans are not open to this objection.] 



[Note. — These thermometers being new in plan, particiiltir instructions in regard to 

 suspending and setting tliem will be given with each instrument by the maker, Mr. 

 James Green, New York.] 



