1893.] TFTE MICROSCOPE. 89 



the same amount of ground, and at the same cost of labor, 

 in almost any other way. 



Such excessively high-bred varieties are, of course, very 

 sensitive to surrounding influences. They thrive best in light, 

 rich, loamy soils, and in moist, equable climates, as notably in 

 some portions of England. In poor soils they speedily de- 

 generate into a weedy and acrid state; while liberal use of suit- 

 able manures has been known to raise their yield from two up 

 to twelve tons per acre. They are, likewise, comparatively 

 helpless against foreign attacks, becoming the easy prey of the 

 turnip-fly and beetle ; whole fields being often blighted, al- 

 most at once, by mildew fungi (Peronospora parasitica and Oidi- 

 um balsamii). Nearly all these points will be found explained, 

 or at least hinted, in the very simple object on the slide. 



-ooo- 



ON ILLUMINATION FOR PHOTOMICROGRAPHY. 



BY F. W. MILLS, HUDDERSFIELD, ENGLAND. 



The Author of an " Introduction to the Study of the Diatomacese. v 

 From "Photography Applied to the Microscope." 



The illuminant may be either (1) oxy-hydrogen lime-light, 

 (2) coal gas, (3) paraffin, or (4) day light. The oxy-hydrogen 

 light is probably the most convenient for the majority of 

 workers, two forms of jet being available, (I) the "blow- 

 through," (2) the mixing jet. The former is the safest for 

 beginners to work with, the oxygen gas being blown through a 

 hydrogen flame upon the lime cylinder, but the light is not 

 so good as that obtained from the latter, in which the oxygen 

 and hydrogen are mixed in a chamber, previous to consump- 

 tion at the nozzle. The nozzle of this jet should be fine in 

 bore, rather finer than when for use in the lantern ; by this 

 means a nearer approach is obtained to the theoretical " point 

 of light." A very good mixing jet, invented by Mr. Andrew 

 Pringle, is provided with a special cut-off tap which, in one 

 movement, cuts the oxj^gen off completely, and turns, at the 

 same time, the hydrogen down to a minimum. The limes 

 should be of the hardest description. All good jets are pro- 

 vided with an arrangement for turning the limes when they 

 become pitted, for if their use be continued in this state, the 

 flame is liable to spurt sideways, and so crack the condenser. 

 The gas for the jet can be obtained compressed in steel cylin- 

 ders. 



In our own case we use the oxygen from a cylinder provided 



