120 John Adie, Esq., on the Marine Telescope. 



exact place of which was not known previous to its use. In 

 these experiments a lenticular form of glass was made use 

 of at the bottom of the tube, having a plane surface to the 

 water, but no great or marked advantage was observable from 

 this construction. With respect to the history of this con- 

 trivance for viewing the bottom of the sea, we are unable to 

 assign any particular date : so far as our information goes, it 

 has been in use from a very remote period. We are informed 

 that it is in general use in seal-shooting along our northern 

 and western islsftids, where, sometimes in the form of an 

 ordinary washing- tub, with a piece of glass fixed in its bot- 

 tom, the shot-seal was looked for, and the grappling- hook 

 let down to bring him to the surface. It may not be gene- 

 rally known, that in seal-shooting, the shot or wounded seal 

 always seeks the bottom, from which he never rises after 

 death, till washed ashore by the action of the sea : it is only 

 when the fatal ball deprives him of the power of diving that 

 he is ever found at the surface. In such employments, there- 

 fore, the use of this instrument, however modified, must form 

 an important auxiliary to the best rifle. Throwing oil over 

 the surface of the water is used in the same pursuits ; but this 

 only so far stills the ripple, leaving the reflections. Our 

 eminent engineer, Mr Robert Stevenson, made use of the 

 water- tele scope more than 30 years ago, in works connect- 

 ed with harbour improvement in the north of Scotland ; it 

 has also been used to examine the sand-banks, &c.j at the 

 bottom of the River Tay, but in this case the mud prevented 

 its use in any considerable depth of water. To obviate this 

 difficulty, the construction was modified thus : by making 

 the tube of considerable length, and placing the glass at the 

 lower end, this tube was thrust through tho water till within 

 a few feet of the bottom, acting as a coff*erdam to set aside 

 the dirty water, and enable the bottom to be seen ; but in 

 this method of application it was found very difficult to hold 

 the tube down in the water from its buoyant power, and we are 

 informed by Mr Thomas Stevenson, C.E., that, he understood 

 from tliis cause its use had been discontinued. He sug- 

 gested a simple remedy ; viz., to fill up the empty tube with 

 pure water. We are indebted to Mr Mitchell, the gentle- 



