188 Scientific Intelligence. Meteorology. 



rained experimentally at what precise temperature the watch is 

 regulated, that is to say, at what degree the seconds* hand beats 

 exactly 86. 400 times in the twenty-four hours, the difference 

 between 86.400 beats and the real number of oscillations which 

 it makes during the twenty-four hours of any given day will 

 afford the data for calculating its mean temperature, whatever 

 may have been its variations throughout the several periods of 

 which the day is composed. Each temperature, in truth, having 

 acted according to its intensity and duration, will be expressed 

 in the beats of the seconds 1 hand in the total result, and may 

 form the expression in an exact arithmetical calculation of the 

 mean temperature, just as if the elements of that temperature 

 had been known. All, then, that will be required will be for the 

 observer, twice in the twenty-four hours, to note the difference 

 of the strokes of the pendulum of a well regulated chronometer 

 and the thermometer-watch, and this will furnish the daily ac- 

 celeration or retardation of the latter. Astronomers will be 

 aware that the uncertainty in these comparisons will be only to 

 the extent of a very small fraction of the oscillation. It will be 

 easy experimentally to construct a table which will convert the 

 quicker or slower movement of the watch into the degrees of the 

 common thermometer. For the purpose of rendering this watch 

 more generally useful, M. Jiirgensen has connected with it, and 

 without sensibly augmenting its size, a metallic thermometer 

 which gives the actual temperature ; arid, with the aid of two 

 floats, the maximum and minimum temperatures that occur du- 

 ring the twenty-four hours. The idea of employing an uncom- 

 pensated pendulum to measure the annulative effect of tempera- 

 ture was suggested by Brewster many years ago, and more late- 

 ly in Germany by Grassmann. 



2. Extract of a Letter from M. to M. Arago, upon 



tlie Shooting Stars of the year 1695. After having read your 

 article upon Shooting or Falling Stars in the Annuaire of the 

 present year, I met, in the course of my reading, with a fact 

 which goes to support the statement you advance, that the 

 shooting stars have been especially observed in the months of 

 April and November. I was then reading Wilkin's work, in 

 which he has supplied the learned world with the best history 

 we possess of Crusades. In giving an account of several phe- 



