250 THE AMERICAN MONTHLY [Sep 



blow-through jet, would take about three minutes to be 

 sufficiently exposed with a round-wick lamp. 



The straight-wick lamps, used edge-on, work quicker, 

 but it is more difficult to get even illumination with them. 



In many cases when photographing very delicate or un- 

 stained specimens, an oil light is of the greatest service, 

 and will be found to give better results than can be ob- 

 tained by modifying the brilliancy of the lime-light with 

 several screens. 



Lime-light is often used to quicken the exposure, to pre- 

 vent the blurring of the image due to vibration. 



I have come to the conclusion that vibration has been 

 greatly over-estimated, and cannot conscientiously say 

 that any one of my photographs has shown a blur from 

 this cause ; it is more honest to put the want of sharpness 

 down to bad focussing, if care has been taken to render 

 the image as perfect as possible, optically, by focussing 

 the substage condenser, and correct the objective by col- 

 lar or tube. 



Vibration may occur if one is working in a house near 

 a railway, or very near a thoroughfare where the traffic 

 is thick and heavy, but in ordinary circumstances it is the 

 writer's opinion that any floor of a house or building may 

 be used, and that if the apparatus be placed on a firm ta- 

 ble, and the legs of the table be supported on layers of 

 felt, no blurring of the image will be found to occur due 

 to vibration ; but, in nine cases out of ten, it will be due 

 to incorrect focussing, or to some carelessness on the part 

 of the operator, such as jerking the apparatus when pull- 

 ing out the dark slide. 



A good way to insulate the legs of the table is to have 

 blocks of wood about four inches high each with a hole 

 about three inches deep, and rather larger than the part 

 of the leg nearest the floor. 



Cut some circular wads of felt and slip them into the 

 holes, then place these blocks so that the legs of the ta- 



