506 REPORT— 1889. 



case sliould have read higher than the one with the thin case ; it, however, gave 

 readings 1'6° F. lower. But it must be remembered that the thick case transmitted 

 less than half as much of the radiation from the gas flame as passed through the 

 thin case, so it must have stopped more of the radiation from the sun than the thin 

 case, and notwithstanding this the temperature registered is very little less than that 

 indicated by the other instrument. 



The small bulb instrument has another advantage over the large bulb one, 

 inasmuch as it is much more sensitive, and so reaches the maximum more quickly 

 than when a large bulb is used. This is shown by the readings on August 4, when 

 there were only some occasional gleams of sunshine, the large bulb registering 

 98-2° F. and the small bulb 101-8° F. 



It seems to follow from these experiments that the black bulb should be as small 

 as possible, and very little of the stem blackened ; and also that the case should be 

 as thin as is consistent with strength. 



A series of experiments should be carried out with instruments of different 

 sizes and with cases of different thickness in order to set the matter at rest. Some 

 investigations on this subject have been carried on at the Kew Observatory, but I 

 believe they have been only partially published. An accident to our old instru- 

 ments gave me the opportunity of having fresh ones constructed, and it seemed 

 advisable to put the above results on record. 



5. Fifth Report of the Committee for considering the hest means of Gomfariny 

 and Reducing Magnetic Observations. — See Reports, p, 49. 



6. On Atmospheric Electricitg. By Professor Leonhard Weber. 



The continuous currents obtained on clear days by flying kites and balloons 

 were investigated, and deductions as to the rate of variation of potential with 

 elevation were made. 



7. Electrification of Air hy Comhustion} 

 By Magnus Maclean, M.A., F.B.S.E., and Makita Goto. 



This was a description of a large series of experiments on natural atmospheric 

 electricity carried on, under the instructions of Sir "W. Thomson, in several of the 

 rooms of the University of Grlasgow. Their purpose was to find a relation between 

 the electrification of the air within a room, and the potential of the air in its 

 neighbourhood outside ; and also the causes which produce or change the electri- 

 fication of air within an enclosed space. 



An insulated water-dropper and a Thomson's quadrant electrometer were used 

 in the usual manner, but the deflections were observed by a telescope instead of by 

 lamp. It was found that an enclosed mass of air is electrified negatively by the 

 burning of a paraffin lamp, of coal gas, of sulphur, of magnesium, and of several 

 other substances. On the other hand, the burning of charcoal electrified a room 

 positively. 



An arrangement was also described bj-- means of which the burning substance 

 was joined metallically to one of the quadrants of the electrometer, and precautions 

 being taken to guard against the efi'ect of the surrounding air, it was found that the 

 substances which electrified the air negatively became positively electrified them- 

 selves. Thus burning charcoal was found to give a deflection equivalent to three 

 volts in the negative direction, the other terminal of the electrometer being joined 

 to the case of the instrument and to earth. 



Electrician, September 20, 1889. 



