340 MR BLACKADDER on Meteorological Instruments 



thod by which it seemed probable that these might be overcome 

 or obviated. It was not, however, till within the last eighteen 

 months that circumstances permitted my bringing that method 

 to the test of experience. 



For upwards of a year I have been in the daily habit of using 

 a thermometer, the indications of which may be registered at any 

 given instant, during absence, and so as to render the tenth of a 

 degree on Fahrenheit's scale readily distinguishable. Suppose, 

 then, a gentleman occupied in keeping a register of the varia- 

 tions of atmospheric temperature, taking two observations in 

 the course of the day, say 10 A. M, and 4 p. M., which, if not the 

 most proper, are about the most convenient hours. To carry on 

 his register, he must be at home and disengaged every day, and 

 exactly at these hours, which must be exceedingly irksome, if at 

 all possible, for any length of time ; or he must every now and 

 then trust to others, little skilled perhaps, or in no way interest- 

 ed in such pursuits, circumstances sufficient to render the whole 

 register defective. By the method which I have to propose, this 

 obstacle is completely obviated. For the observer may be from 

 home many hours before and after the hour fixed upon for not- 

 ing his register ; and, on his return, he shall find the tempera- 

 ture of that hour exactly registered by the instrument. 



If we can thus succeed in effecting a register of one observa- 

 tion at a given instant during absence, it is obvious that we may 

 so adapt matters as to have a register at successive intervals, 

 say at the distance of one hour, half an hour, or two hours, be- 

 tween each ; and I shall presently have an opportunity of demon- 

 strating, that, with very little trouble, we can thus ascertain the 

 exact temperature every hour during the whole course of the day 

 and night. 



If, again, a gentleman wished to carry on a set of ex- 

 periments at two or more places at the same time, such as by 

 the sea-shore, and at some inland situation, or at the foot and at 



