In the inclosed, you have all I have to say of that matter[5]. It proved longer than I expected, so that I was forced to add a cover to it. I confess it looks like a dispute; but that is quite contrary to my intentions.
The sincerity of friendship and esteem were my motives; nor do I doubt your scrupling the goodness of the intention. However, I must confess I cannot tell exactly how far I was acted by hopes of better information, in discovering the whole foundation of my opinion, which, indeed, is but an opinion, as I am very much at a loss about the validity of the reasons. I have not been able to differ from you in sentiment concerning any thing else in your Suppositions. In the present case I lie open to conviction, and shall be the gainer when informed. If I am right, you will know that, without my adding any more. Too much said on a merely speculative matter, is but a robbery committed on practical knowledge. Perhaps I am too much pleased with these dry notions: however, by this you will see that I think it unreasonable to give you more trouble about them, than your leisure and inclination may prompt you to.
I am, &c.
Since my last I considered, that, as I had begun with the reasons of my dissatisfaction about the ascent of water in spouts, you would not be unwilling to hear the whole I have to say, and then you will know what I rely upon.
What occasioned my thinking all spouts descend, is, that I found some did certainly do so. A difficulty appeared concerning the ascent of so heavy a body as water, by any force I was apprised of, as probably sufficient. And, above all, a view of Mr. Stuart's portraits of spouts, in the Philosophical Transactions.
Some observations on these last will include the chief part of my difficulties. Mr. Stuart has given us the figures of a number observed by him in the Mediterranean: all with some particulars which make for my opinion, if well drawn.
The great spattering, which relators mention in the water where the spout descends, and which appears in all his draughts, I conceive to be occasioned by drops descending very thick and large into the place.
On the place of this spattering, arises the appearance of a bush, into the centre of which the spout comes down. This bush I take to be formed by a spray, made by the force of these drops, which being uncommonly large, and descending with unusual force by a stream of wind descending from the cloud with them, increases the height of the spray: which wind being repulsed by the surface of the waters rebounds and spreads; by the first raising the spray higher than it otherwise would go; and by the last making the top of the bush appear to bend outwards (i. e.) the cloud of spray is forced off from the trunk of the spout, and falls backward.
The bush does the same where there is no appearance of a spout reaching it; and is depressed in the middle, where the spout is expected. This, I imagine, to be from numerous drops of the spout falling into it, together with the wind I mentioned, by their descent, which beat back the rising spray in the centre.