183 



is of brass divided to degrees. " Newman (Makerstoun)" is the in- 

 strument wliich was supplied to the Makerstoun Observatory as a 

 standard, and to whose indications the results of the temperature 

 observations made there since 1841 have been " corrected." It was, 

 at my suggestion, sent to Kew by Sir Thomas Brisbane for compa- 

 rison with our standards. " Troughton and Simms (Royal Society) " 

 is a standard belonging to the Royal Society. As its scale extends 

 to above 212, its boiling-point was examined in the same apparatus 

 employed for the Kew standards, its brass scale remaining attached 

 to the tube. It w^as found to read 2 12°- 7 when the barometer, re- 

 duced to 32°, stood at 30-136 inches. 



The errors of a thermometer which has been already carefully 

 examined between 32° and about 100°, may be obtained with con- 

 siderable accuracy for temperatures below 32°, without using a free- 

 zing mixture, by the following process. Detach from the column of 

 mercury a portion which will occupy about 40 or 50 degrees of the 

 scale : bring this column within the known part of the scale. Let 

 a, b be the readings at the upper and lower ends respectively ; a, /3 

 the index errors at these points as determined by comparison with 

 a standard. Move the column until its lower end coincides with 

 some degree below 32°, the upper end being within the compared 

 portion of the scale. Let c, d be the scale-readings for the upper 

 and lower ends in the new position, y being the scale error corre- 

 sponding to c. The error of the scale at d will then be 



d- {c-y- (a-a- h^0) } • 



The true length of the detached column may be obtained with in- 

 creased accuracy by taking a mean of several measures within the 

 known part of the scale. This method was adopted for " Newman 

 (Makerstoun) " and " Troughton and Simms (Royal Society)," and 

 the following errors obtained : — 



Newman (Makerstoun). Troughton and Simms (R.S.). 



Temperature. Error. Temperature. Error. 



6-7 -6-05 5 1 +6-14 



6-2 -0-0.8 10-0 -i-0-17 



10-7 -0-12 15-0 +0-16 



14-6 -0-10 20-0 -1-0'16 



20-2 -0-04 24-8 +0'16 



25-8 0-00 



The error of " Newman" had been previously found, by comparing 

 with a standard in a freezing mixture at —3°, to be inappreciable. 



Mr. Welsh's Report, No. 2. 



" On the Graduation of the Thermometers supplied from the Kew 

 Observatory for the use of the Arctic Searching Expedition under 

 Sir Edward Belcher." 



These instruments were twelve in number, seven mercurial and 

 five spirit thermometers, graduated for low temperatures, The pro- 



>3* 



