According to promise in my last,7 I now return you Dr. Colden’s Letter, for communicating which I am greatly obliged to you. The Dr. dissenting from you, is of opinion, that Sea Clouds are less electrified than Land Clouds, and gives the reasons of his opinion “That Salt, tho’ an Electric per se, is never raised in Sea-vapours, therefore Sea-Clouds are less electrified than Land Clouds; That all Sulphurs (which mountains especially abound with, from whence Thunder-Gusts are often observed to rise) being Electrics per se, sulphureous vapours are more electrified than Sea-vapours: The conclusions from these reasons might be just, if the Supposition they are form’d upon, was just viz. that vapours &c. are more or less electrified according to the quantity of Electrics per se they contain. But that seems contrary to experience: for Electricity (to instance) is accumulated upon the Conductor without any mixture of the Electrics per se (Glass or Sulphur) which excited it.

Another reason the Dr. offers is, that Electricity forwards vegetation, which makes it probable, he supposes that vapours from the Land and Vegetables are more electrified than Sea-vapours: but by the same way of reasoning, it is probable that Land vapours have a mixture of Salt (which the Dr. has denied and justly I believe even of Sea-vapours) for Salt in a suitable proportion, I have heard, promotes vegetation.

I pretend not to say what vapours are most electrified, but only that these Reasons do not appear to me to support the Dr.’s Opinion. The Doctor hints that he has something in speculation which will be the means of improving all parts of natural philosophy. If he has communicated his Scheme to you, or any new improvement I shall be obliged, provided it be consistent with the Laws of friendship, if you’d favour me with some account of it. I have heard that several Gentlemen have desired you to procure them a number of large glass Jars suitable for electrical experiments; I take the Liberty of adding to your trouble by asking the favour of you to procure half a dozen of them for me, two of them to be coated, and made fit for use, the other 4 I shall get finished here: for which I shall take care to re-imburse you. I am with much esteem Sir Yours &c.