The various sounding instruments that have been invented are divided into two classes; one of which measures the depth of the water by the length of line drawn out by the lead, while those of the other class measure the deptii of the water by the number of revolutions made bj' spiral blades in their vertical descent through the water. The apparatus here illustrated belongs to the latter class, and the improvement in it over those of the same class heretofore in use consists in the plan far connecting the revolving screw with the registering wheels. The former method has been to> prevent the screw from turning in its ascent, thus causing a great drag upon the line; but by this invention the screw is detached from the registering apparatus when it reaches the bottom, and is permitted to revolve freely during its ascent, thus diminishing materially the friction and the strain upon the line. ID the cut, a represents the sounding line, B, the' lead, C, the revolving' screw, and D the register' ing apparatus. The latter is placed in a broad* flat box or plate, which is made in this form to prevent it from being turned1 with the screw. A loose collar, e, is placed on the" spindle, with a worm upon its surface gearing into the pinion, /, of the registering wheels. This-collar is allowed to turn freely on the spindle, but is prevented from slipping up and down by a tongue secured to the box, D, which tongue presses into a groove in the collar. Thus: as the serew, D, is dragged by the lead, B, down through the water, its revolution slowly turn the graduated wheel of the registering apparatus, and the number of fathoms of water which the apparatus pusses through in its descent is recorded. When the bottom is reached, nnd the upward pressure of the water against the blades of the screw ceases, the screw slips down by its own weight on the spindle against the shoulder at its lower cud, thus disengaging the ratchet which is attached to the upper end of the screw from its hold upon the corresponding ratchet on the lower end of the collar, e, and permitting the screw to revolve as the apparatus is drawn up, without turning the registering wheels. In using this apparatus, it is not necessary to stop the ship in order to obtain soundings, care being requisite merely to pay out the line with sufficient rapidity to enable the apparatus to sink vertically through the water. This apparatus seems to us to possess decided advantages over any other of its class that we have examined; all the pans being very simple in their arrangement, and the serious evil of the great drag on the line in recovering the lead being greatly diminished. The patent for this invention was secured (through the Scientific American Patent Agency) Nov. 27, I860; and further information in relation to the matter may be obtained by addressing the inventor, J. B. Van Deu-sen, at No. 246 Seventh-street; or E. & G. W. Blunt, the well-known nautical instrument makers, No. 179 Water-street, this city. SCIENCE IN CANADA.We are pleased to acknowledge the receipt, from the Hon. L. A. Dassaulles, Member of the Legislative Council of Canada, of a number of valuable public documents. They consist of Reports of the Superintendent of Education, of the Inspectors of Asylums and Prisons, of the Commissioners of Pal lie Works, of the Board of Railway Commissioners, of the Commissioner of Crown Lands, and of the Geological Exploration. The last is accompanied with large and minute maps which extend westward to the Pacific, and northward to the entrance of the open polar sea discovered by Dr. Kane, and tell, at a glance, the story of an immense amount of labor that has been expended in these geological surveys. All the documents furnish forcible evidence of the rapid material and intellectual progress of Canada. A SERIES of experiments have recently been completed at the United States Mint at New Orleans, to test the amount of abrasion which coins undergo by wear. It was found that the thin coins underwent less wear than the thick ones; Spanish quarter dollars les than American ones, and the thin one dollar gold pieces most recently issued, lest than those older and thicker.