90 THE MICROSCOPE. July, 



with a regulator which renders the adjustment of the flame 

 possible at the taps of the burner ; but take the hydrogen 

 from the mains — or rather, we ought to say, we use coal gas 

 for hydrogen — the only danger in this method of working is 

 that the oxygen must be turned on carefully, as otherwise it 

 may be blown round into the mains, and thus extinguish the 

 light at the jet, and form, into the bargain, a pleasant surprise 

 for the next person who attempts to light the gas in another 

 part of the house ; but with care this cannot happen. Using 

 ordinary coal gas alone as an illuminant, we have used an 

 Argand burner with fair success, but found it not so good as a 

 Welsbach flame, which is a Bunsen flame playing upon the 

 interior of a cap made of cotton fibre netted and coated with 

 a mixture of metallic salts, chiefly oxide of zirconium. We 

 have also at a press used a common fish-tail burner screwed 

 into the position of the nozzle of the mixing jet. this device 

 being used when we ran short of oxygen, but it is difficult, by 

 this means, to obtain a good enough light to work with any 

 but very low powers. 



An ordinary paraffin microscope lamp is also available, but 

 is better suited for low powers than high. 



Day light requires special arrangements scarcely within the 

 reach of ordinary amateurs ; a heliostat is needed to keep the 

 sunlight upon the condensers. The heat from this illumin- 

 ant must be cut off by using ammouio-sulphate of copper 

 cell. 



In our our own practice we use a four-inch condenser, out of 

 an optical lantern, to collect the rays from the source of illu- 

 mination, and so arrange it that it thrown a converging pencil 

 of rays, the apex of this cone being in the diaphragm of the 

 microscope. When colored screens are used, they are placed 

 between the light and this four-inch condenser, this position 

 having two advantages which are, (1) small imperfections in 

 the glass are of no consequence, (2) and if the flame should 

 spun sideways it is better to lose this glass than an expensive 

 condenser. In order to do away with vibration of passing 

 traffic, etc., being transmitted to the instrument, we place it 

 on two rolls of cotton w r ool ; one supporting each end of the 

 microscope board. 



-ooo- 



PRIZES TO BE AWARDED FOR ORIGINAL WORK WITH 



THE MICROSCOPE. 



The following sums of money have been placed at the 

 disposal of the American Microscopical Society, to be given 



