Did you ever see People at work with Spades and Pickaxes, digging a Cellar?

When they have loosen’d the Earth perhaps a foot deep, that loose Earth must be carried off, or they can go no deeper; it is in their way, and hinders the Operation of the Instruments.

When the first foot of loose Earth is removed, they can dig and loosen the Earth a foot deeper.

But if those who remove the Earth, should with it take away the Spades and Pickaxes; the Work will be equally obstructed as if they had left the loose Earth unremoved.

I imagine the Operation of Fire upon Fewel with the Assistance of Air may be in some degree similar to this. Fire penetrates Bodies, and separates their Parts. The Air receives and carries off the Parts separated, which if not carried off would impede the Action of the Fire. With this Assistance therefore of a moderate Current of Air, the Separation encreases; but too violent a Blast carries off the Fire itself; and thus any Fire may be blown out as a Candle by the Breath if the Blast be proportionable.

But if Air contributes inflammatory Matter as some have thought, then it should seem, that the more Air, the more the Flame would be augmented, which beyond certain Bounds does not agree with the Fact.

Some Substances take Fire, i.e. are kindled by the Application of Fire much sooner than others. This is in proportion as they are bad or good Conductors of Fire, and as their Parts cohere with less or more Strength. A bad Conductor of Fire not easily permitting it to penetrate and be absorb’d and its force divided among the whole Substance, its Operation is so much the Stronger on the Surface to which it is apply’d, and is in a small Depth of Surface strong enough to produce the Separation of Parts which we call Burning. Wax, Sulphur, all Oils and Fats and most vegetable Substances are bad Conductors of Fire. The Oil of a Lamp, burning at the Top may be scarce warm at the Bottom; a Candle or a Stick of Wood inflam’d at one End is cool at the other. Metals which are better Conductors are not so easily kindled, tho’ when sufficient Fire is apply’d to them to separate their Parts they will all burn. But the Fire apply’d to their Surfaces enters more easily is absorb’d and divided; and not enough left on the Surface to overcome the Stronger Cohesion of their Parts. A close Contact with Metals will for the same Reason prevent the burning of more inflammable Substances: A flaxen Thread bound close round an Iron Poker, will not burn in the Flame of a Candle; for it must imbibe a certain Quantity of Fire before it can burn, i.e. before its Parts can separate; But the Poker as fast as the Fire arrives, takes it from the Thread, conducts it away and divides it in its own Substance.

Common Fire I conceive to be collected by Friction from the common Mass of that Fluid, in the same manner as the electrical Fluid is collected by Friction, which I have endeavoured to explain in some of my electrical Papers, and to avoid Length in this Letter refer you to them. In Wheels the Particles of Grease and Oil acting as so many little Rollers and Preventing Friction between the Wood and Wood, do thereby prevent the Collection of Fire. [Elsewhere on this page arranged in a column:] Col Ludwell / Call at John Hunts / Mrs French / Dr Russell / Wm Do [ditto] / Elias Bland / Brown Charter house / Mr Colepeper / Henry & Cave / Dr Bevis / Mr Wilson Canon street / Newbery / Crosson / Mildred / Aufrere / Sargent / Neat & Neave / Collinson / Post Office / Baker Cards Exp[enses?] / Willock / Dr Reeves / Dr Hadley / Mr Edwards / Memo. Becket Tully Old Age / Ephemerides Motuum / Mr Allen and Miss Downes [In another column:] Bellows. / Toys for Children / New Things at Turners. / Tin men Pewterers Brasiers.