332 PROCEEDINGS OF THE AMERICAN ACADEMY. 



ing any fluid I have tried, with its contents, whatever they might be. 

 At the same time, neither this nor any other bulky instrument can be 

 a substitute for a simple, portable, vertical instrument, with a horizontal 

 stage, and mirror below it, to be employed with the low powers. It is 

 an adjunct to it, performing all the difficult tasks which the small 

 " comet-seeker " indicates and leaves unfinished. The new instru- 

 ment can be employed with the lowest powers ; most conveniently by 

 using a secondary stage, consisting of a piece of sheet brass bent at 

 right angles, and carrying two springs on its outer vertical surface to 

 hold the object-plate ; this secondary stage being placed on the lamp- 

 shelf. But every microscopist requires a portable instrument which 

 will be sufficient for all powers below the one-fourth inch objective or 

 its equivalent. For twenty dollars or a little more, he can get such an 

 instrument with two eye-glasses and two objectives. Let him add 

 twelve dollars to this, and he can obtain, in addition, the highest ob- 

 jective of the French makers. With the addition of an instrument 

 like that I have shown, he will have at his command a sufficiently 

 complete series of powers, and the means of employing common and 

 achromatic light in every degree of intensity and obliquity, with a bril- 

 liancy of effect and a convenience in application which I will venture 

 to compare with those of much more costly instruments. If he can 

 obtain the more perfect and expensive objectives of Mr. Spencer or 

 the best London makers, he will be able to bring out all their powers, 

 and need not fear to subject them to the trial of defining the most 

 difficult test objects." 



Professor Horsford made some additional remarks on the 

 subject of the late explosion of burning-fluid at Salem. On 

 further consideration, he was of opinion that the ascent of 

 heated air above the stove would cause currents of air to de- 

 scend by the sides of the pantry, and flow towards the stove ; 

 and that the vapor of burning-fluid would be thus carried 

 towards the fire, and ignition consequently ensue. He also 

 off'ered an explanation of several other cases of explosion of 

 burning-fluid to which he referred. 



