PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 395 



the gentleman will bring his box here at the next meeting, I will have a 

 man here who will open it before us all. It will be rather interesting. 



Shaw's Sash Lock. 



jMr. Allen. — This is a model of Shaw's sash supporter and lock. A pinion 

 is secured in the window frame and works in a rack secured to the edge 

 of the sash. The pinion is provided with a small catch to hold it from 

 turning; the catch having a thumb piece for pressing it from its hold 

 whenever it is desired to raise or lower the window. For a heavy sash a 

 coiled spring is attached to the pinion, to counteract the weight of the 

 sash. The arrangement is a great deal cheaper, more compact, and less 

 likely to get out of order than the ordinary arrangement of cords and 

 weights. It will save 175 per cent. 



Mr. Adriance. — There is inaccuracy in the language in talking about a 

 saving of 175 per cent. If a man saves lUO per cent, he saves the whole 

 and of course can save no more. If the old style of window cost one dol- 

 lar and this can be made for 25 cents, then this will eflect a saving of 75 

 per cent. But if we wish to say how much more the old window costs 

 than this, then we say it cost 300 per cent. more. In one case the per cent- 

 age is reckoned on the dollar, in the other on the quarter. 



Photographic Printing Machine. 



Mr. Fontaine. — This is a machine for printing photograph positives from 

 the negative. It looks, you see, something like a small wooden trunk. 

 The negative is secured in the upper part of the lid, directly below an open- 

 ing tiu-ough which the light enters, the light passing through the negative 

 as usual, and forming a reversed copy or positive upon the sensitive paper 

 below. The sensitive paper is wound on this shaft and is turned under the 

 opening by a crank. The negative is secured by a spring at one edge, and 

 is pressed down in contact with the positive paper for a moment while the 

 paper is stationary, and at the same instant the orifice for the light is 

 opened by the hole in the revolving plate above it coming over the orifice. 

 It will print four pictures a second, whicli is at the rate of 14,400 per hour. 

 These sheets were printed with the machine, and I will pass them around 

 for inspection. By condensing the light by a lens, 30,000 pictures per 

 hour may be printed. 



Tiie Chairman.— I see Prof. Seely present; will he please to give us his 

 opinion of this machine ? 



Prof. Seely. — I admire the mechanical ingenuity displayed in the con- 

 struction of the machine. The process employed is that which Talbott em- 

 ployed in 1840. It has been repeatedly tried, but is not now used to any 

 extent. 



Mr. Fisher. — How much time is occupied in changing the sheets ? 



Mr. Fontaine.— With one assistant (my daughter, who is 18 years old) I 

 can print and finish 350 positives per hour. 



Mr. Stevens. — Could this process be used for illustrating a book ? I ask 

 this question in reference to a work now in manuscript of an acquaintance, 

 who is delaying its publication on account of the illustrations. The work 

 is on physiognomy. Heretofore works on this subject have been illustrated 



