VOL. XLV.] PHILOSOPHICAL TRANSACTIONS. 4gg 



to a brittle charcoal, by the heat of the inch-depth of earth which lay on it, which 

 hindered the burning board from flaming. And it was observable that the edges 

 of the board burnt only with a live coal like a match ; being hindered from flam- 

 ing by the earth which lay on the board. 



May it not hence be reasonably inferred, that when a house is on fire, it may 

 be a probable means considerably to retard the progress of the fire, to cover with 

 earth the floors of the adjoining and more distant houses, which stand in the 

 course of the progress of the flames ? The thicker the earth is laid so much the 

 better : but if time will not permit to lay it more than an inch thick, then sup- 

 posing 27 men to carry each a cubic foot of earth, which will be a cubic yard of 

 earth; then that cubic yard of earth will cover 36 square yards of flooring; which 

 repeated several times, would soon cover all the floors of a house. And as the 

 fire probably mounts with great fierceness up the staircase, it will be well to lay 

 much earth on the stairs ; which will help to give some check, especially as the 

 earth on the floor and stairs may be wetted by the fire-engine ; which moisture 

 will be much the longer retained by means of the earth ; whereas water, when 

 not thus retained, soon glides away. 



And as fires often catch from house to house at their upper parts, an upper 

 floor covered with earth, vvith the rafters burning on it, will be longer in burning 

 to such a degree as to fall on the next floor, so when fallen there, it will also be 

 the longer in burning, and will flame the less, on account of the earth on that 

 next floor ; and consequently will not be so apt to fire the next house, as in the 

 common case of floors without earth, which must needs therefore burn the more 

 fiercely. 



Note by Dr. Mortimer . — Two days after the fire-works had been played off in 

 the Green Park on account of the late peace. Dr. M. went all over the building 

 erected for that purpose, and was greatly pleased to see the Doctor's scheme con- 

 firmed by the practice of the engineers on that occasion ; for the rooms in which 

 the trains were fired, and which was immediately under the gratings on which 

 the 6CXX) rockets rested and were fired from, had the floor covered over with fine 

 sifted gravel about an inch deep, and the walls were whited over with a dirty sort 

 of white wash, which he took for lime finely powdered, and mixed up with size 

 and water, and done 2 or 3 times over. Both floors and walls were of deal. 



Observations made during the last Three Years, 0/ the Quantity of the Variation 

 of the Magnetic Horizontal Needle to the Westward. By Mr. George Gra- 

 ham, F.R.S., at his House in Fleet-street, London. N° 487, p- "i-TQ- 



1745 March 26 17° O' 1745 March 21 . . 



29 17 O April 22 . , 



March 18 17 10 May 4 . . 



3 s 2 



