PHYSICS OF THE GLOBE. 67 



most important instrument to those engaged in investiga- 

 tions bearing on the growth and distribution of plants, as 

 well as to the physical meteorologist. 



The importance of knowing the sum total of the tempera- 

 tures at any place for various meteorological and phamolog- 

 ical studies, lends value to the suggestion of Steinecke that 

 clocks uncorrected or anti-corrected for temperature be in- 

 troduced as a part of the meteorological apparatus. Such 

 clocks or chronometers, called thermo- chronometers, have 

 lonor been used in lono-itude determinations and for ratine: 

 chronometers, and will abundantly answer the required 

 purpose. But for meteorological purposes, self-recording 

 thermometers, in connection with Ausfeld's planimeter, offer 

 every facility for accomplishing the same end cheaper and 

 better. The idea of temperature clocks is also worked up 

 by Mr. F. Stanley in the Quarterly Journal of the London 

 Meteorological Society. 



Of the numerous precautions to be taken in using the wet- 

 bulb thermometer, we find some account in Marriott's report 

 detailing the results of observations on ten wet and three 

 dry thermometers all enclosed in the same cage. It is neces- 

 sary that all should be covered with the same kind of mus- 

 lin, which should be very thin, and be connected with the 

 water reservoir by six or eight threads of yarn tied to the 

 upper end of the muslin. For the minute yet important de- 

 tails we must refer to the volume itself. 



The formulae for correction of the instrumental errors of 

 the aneroid are given by Von Wullerstorff Urbain, who ex- 

 emplifies them by an example drawn from the record of the 

 ship Tegetthoff. 



In the course of his remarkably accurate investigation 

 into the truth of the Boyle or Mariotte law, Mendelleff in- 

 vented an improvement upon the barometer undoubtedly 

 one of the most important that has ever been suggested. 

 It consists simply in terminating the upper end of the ba- 

 rometer tube by a capillary tube bent downward. By means 

 of this it is possible to cut off and expel the last trace of any 

 foreign gas that may remain in the vacuum chamber. He 

 thus obtains a perfect instrument Avithout boiling the mer- 

 cury in the tube. His determination of the correction for 

 capillarity and his method of measuring the barometric press- 



