298 Mr. Blackwall's Thermometrical Observations. [Oct. 



of the sun, about a foot from the window of a room on the second 

 floor, having a northern aspect. 



The preceding observations were made with the common mer- 

 curial thermometer: the first, at 12 o'clock on the night of the 

 14th, and one each succeeding half hour, to 12 o'clock on the 

 night of the 15th, making a total of 49 observations. 



The state of the weather during the whole of this period was 

 as follows : From 



Midnight on the 14th to half-past two, a. m. on the loth, 

 clear and starlight. 



Half-past two, a. m. to half-past three, clear and fine. 



Half-past three to four, hazy. 



Four to half-past six ; dense fog. 



Half-past six to eight, foggy. 



Eight to nine, hazy. 



Nine to eleven, hazy, with clouds and faint sunshine. 



Eleven to one, p.m., sunny, with some light clouds. 



One, p. m. to half-past one, cloudy, with a little faint sunshine. 



Half-past one to half-past two, overcast. 



Half-past two to four, cloudy, with gleams of sunshine. 



Four to half-past five, cloudy. 



Half-past five to half-past seven, cloudy, with gleams of sun- 

 shine. 



Half-past seven to eleven, cloudy. 



Eleven to midnight, moonlight, with a few clouds. 



The wind was SW. aud light, all the time. 



The lowest point to which the mercury descended was 46° ; 

 this extreme it reached at two o'clock, a. m. and remained sta- 

 tionary for half an hour ; when it began gradually to ascend, 

 and reached 67°, its highest extreme, at three o'clock, p. m. 

 The mean of these extremes is 56-50°, and the mean of the 49 

 observations is 56-37°. 



The means of two observations, one taken in the morning, and 

 the other in the evening, that approach the nearest to the mean 

 of the natural day, appear to be those obtained from observa- 

 tions made at 



Half-past seven, a.m. and half-past seven, p. m. the mean of 

 which is 56-35°. 



Eight, a. m. and eighty p. m. the mean of which is 56-35°. 



Nine, a. m. and nine, p. m. the mean of which is 56-25°. 



Half-past nine, a. m. and ten, p. m. the mean of which is 

 56-25°. 



Ten, a. m. and half-past ten, p. m. the mean of which is 

 56-35°. 



The nearest means of three observations seem to be those 

 found from observations taken at 



Half-past seven and half-past ten, a. m. and half-past nine, 

 p. m. mean 56-40°. 



Eight and half-past ten, a. m. and ten, p. m. ; mean 56-40°. 



