A comparison between the two sketches over page will, I think, go far to prove me right, since the so-called "Diver's Helmet" is taken from Vegetius' _De Re Militari_, not published before 1511. The earliest picture of a diving-helmet of this kind I have been able to find is in a German work published in 1500: both are therefore of a later date than the "Swimming Jacket". This "jacket" was intended to be worn as follows: The lower rectangular part was to be placed at the back, the oval portion to the front of the body. When the swimmer wished to remain at the surface he inflated his jacket by means of the tube; when he required to dive out of sight he would let the air out. Look at the position of the buckles and straps in the two drawings and you will see that there is a strong presumption that the later artist deliberately made the alteration in order to support his bogus picture of a diving-_helmet_. [Illustration: Swimming Jacket (from a fourteenth-century MS.) Diver's Helmet from Vegetius (sixteenth century) Observe the close similarity between these two nominally very different articles. The shape of the earlier drawing has suggested a helmet to the illustrator of _De Re Militari_ by Vegetius, and he has therefore done away with two straps and buckles and altered the positions of the other two. It is not clear how they are to be fastened together; but the use of the straps and buckles on the jacket is apparent.] The earliest mention of a submarine boat occurs in "Salman[49] and Morolf", a German poem of 1190. This was, of course, an imaginary one, like the famous _Nautilus_ in Jules Verne's _20,000 Leagues under the Sea_; but in the days of "good Queen Bess" one William Bourne, a naval gunner, published a detailed description of how to make "a shippe or boate that may goe under the water unto the bottome, and so to come up againe at your pleasure". The "device", as he calls it, had some quite practical points.[50] In the following reign a Dutchman, Corneilius Van Drebbel by name, seems actually to have built a submarine vessel, which is stated to have gone under water from Westminster to Greenwich, and with which James I was so pleased that he not only had a duplicate one built, sending it as a present to the Tsar of Russia, but so far overcame his constitutional timidity as to adventure his precious and royal person in a submarine trip in the Dutchman's invention. Then followed many suggestions for submarines, but between Van Drebbel's boat in 1620 and Fulton's in 1800 probably not more than half a dozen were actually constructed. Van Drebbel was probably responsible for the "water mines, water petards, forged cases to be shot with fireworks, and _boates to goe under water_" which Buckingham took with his fleet on the ill-managed and inglorious expedition to La Rochelle in 1626. The water-petards or floating mines were of a very feeble description. The following is a French contemporary account of what they were like.