From Magna Britannia Volume 6 (published 1819)

by Daniel and Samuel Lysons

 "WOLBOROUGH (OR NEWTON ABBOT)

At this place lived Mr. John Lethbridge, not so well known as he deserves to be, as the ingenious inventor of a diving machine, by which he was enabled to recover goods from wrecks at the bottom of the sea, without any communication of air from above. This gentleman appears to have been of the ancient family of his name. In a letter printed in the Gentleman's Magazine,, he states, that, being much reduced in circumstances, and having a large family, he turned his thoughts to some extraordinary method of improving his fortune; and being prepossessed with the notion that it would be practicable to invent a machine to recover goods from wrecks lost in the sea,

He made his first experiment in his orchard, at Newton Abbot, on the day of the great eclipse, in 1715, by going into a hogshead bunged up tight, in which he continued half an hour without any communication of air; he then contrived to place the hogshead under water, and found that he could remain longer without air under water than on land. His first experiment having been thus encouraging, he constructed his machine, with the assistance of a cooper in London. It was of wainscot well secured with iron hoops, -with holes for the arms, and a glass of about four inches in diameter. It required 500 lbs. weight to sink it, lead being fixed to the bottom of the machine for that purpose; and the removal of 15 lbs. would bring it to the surface of the water.

In his letter Mr Symons claimed that  not only had he  invented "the famous diving-engine for salvaging valuable items from shipwrecks " and that the whole idea had been stolen from him by "his cousin L . . . e who had deprived him of both the honour and the profit, but that he had also  made a successful diving boat which h ad enable him to walk underwater, in the river Dart.

It was to this letter that John Lethbridge made the following reply:

Now, whether the assertion proceeds from prejudice, or false information, I will not determine; but whatever may be the motive, I think it incumbent on me to give an answer thereto, which shall be genuine. And , first, as to the diving-boat insisted upon, I shall say nothing of it, having never seen it, nor ever h eard that it was anywise serviceable, but readily agree with Mr. Ley that his account of it is imperfect; and as to the famous diving-engine, which Mr. Ley is pleased to say was invented bv Mr Symons, I take the liberty to aver it is my own invention. It is observable that Mr. Ley is silent with respect to its description; but as it hath been of such singular service to the public, I shall here insert a particular description thereof, with the principal motive of the invention.

Necessity is the mother if invention, and being in the year 1715 quite reduced, and having a large family, my thoughts turned upon some extraordinary method to retrieve my misfortunes and was prepossessed that it might be practicable to contrive a machine to recover from wrecks lost in the sea; and the first step I took towards it was going into a  hogshead, upon land, bunged up tight, where I stayed half-an-hour without communication of air; then I made a trench, near a well, at the bottom of my orchard in this place in order to convey a sufficient quantity of water to cover the hogshead, and then tried how long I could live under water without air-pipes of communication of air and found I could stay longer under water than upon land.

This experiment being tried, I then began to  think of making my engine, which was soon made by a cooper in Stanhope Street, London, of which you have the following description:

It is made of wainscot, perfectly round, about six feet in length, about two foot and a half diameter at the head and about eighteen inches diameter at the foot, and contains about thirty gallons; it is hooped with iron hoops without and within to guard against pressure. There are two holes for the arms and a glass about four inches diameter, and an inch and a quarter think, to look through, which is fixed in the bottom part, so as to be in a direct line with the eyes, two air-holes upon the upper part, into one of which air is conveyed by a pair of bellows, both of which are stopped with plugs immediately before going down to the bottom. At the foot part, there's a hole to let out water. Sometime, there's a large rope fixed to the back or upper part, by which it is let down, and there's a little line called the signal line, by which the people above are directed what to do, and under which  is fixed a piece of timber as a guard for the glass.

I go in with my feet foremost and when my arms are got through the holes, then the head is put on, which is fastened with screws, It requires 500 cwt to sink it, and take  15 pound weight from it, and it will buoy upon the surface of the water. I lie straight upon my breast all the time I am in the engine, which hath many times been more than six hours, being frequently refreshed upon the surface by a pair of bellows"

No contemporary illustration exists of the original apparatus. Several mock-ups have been constructed and tried out from the detailed description supplied by John Lethbridge in the Gentleman's Magazine of September 1749. The sketch above is believed to date from the 19th century and to have  been made by a diver of that time.