(419) 



DISCUSSION OF THE EEEOES OF CBETAIN TYPES OF 

 MINIMUM SPIEIT THEEMOMETEES IN USE AT 

 THE EOYAL ALFEED OBSEEVATOEY, MAUEITIUS. 



By A. Walter, F.E.A.S., 



Chief Assistant. 



(Eead October 31, 1906.) 



Since the year 1902 the corrections to the minimum spirit ther- 

 mometers in use at the Eoyal Alfred Observatory, Mauritius, have 

 been obtained from daily comparisons between the readings of the 

 spirit and the corrected readings of a mercurial Standard ther- 

 mometer, made near the time of minimum temperature, in accord- 

 ance with the results of the " Investigation of the Degree of 

 Accuracy of Self-registering Maximum and Minimum Thermo- 

 meters " published in the " Introduction to the Mauritius Mag- 

 netical and Meteorological Observations for the year 1901 " (p. xxv). 



The present discussion was undertaken at the request of the 

 Director of the Eoyal Alfred Observatory, in view of the occasional 

 large differences between the minimum temperatures, as shown by 

 a minimum spirit thermometer thus corrected, and the lowest points 

 on the thermograms. 



Table I. shows the results of the comparisons made during the 

 month of November, 1905. 



The minimum thermometer, Casella No. 1,470, was mounted in 

 the Thermograph screen with its bulb at a distance of about 1 foot 

 from the mercurial Standard No. 714, which is used to standardise 

 the photographic records of the Beckley Thermograph, as follows: 

 The observer, while reading the Standard, touches for a few moments 

 the bulb of the Thermograph thermometer, thereby causing a slight 

 temporary dislocation in the photographic curve, so that the exact 

 instant at which the Standard is read is recorded. He then reads 

 the spirit of the minimum thermometer. 



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