200 THE AMERICAN MONTHLY [July, 



sugar beet in Europe. The fungus causes a total destruction of 

 beet, it is entirely worthless for sugar. So far the disease has 

 not been reported from other parts of the state, though accord- 

 ing to Prof. Galloway it occurs in Michigan. Rotation of crops 

 should be practiced. Two root crops should never follow each 

 other, Beet Scab, which has also been found in a few cases, 

 appears to be identical with deep scab of potatoes. Sugar beets 

 should never follow potatoes. In both diseases (Beet Scab and 

 Root-rot), care should be used in cultivation. Cultivators and 

 other implements should be kept rigidly clean. Do not pass 

 from a dis«^ased field to one where the disease does not occur. 

 Infectious material is often carried in this way. 



A Slide-Carriage and Object-Finder. 

 By F. L. J. BOETTCHER, 



WASHINGTON, D. C. 



It has no doubt occurred in the experience of many others, 

 as it has in my own microscopical work that some item of 

 minute dimensions, which had been passed over for future 

 study or comparison, could not be found at the moment when 

 it was most needed for examination or for exhibition. This 

 difficulty sometimes becomes particularly embarrassing in the 

 class-room, when after several minutes of fruitless search the 

 vexed preceptor is obliged to confess : " Gentlemen, the thing 

 which we are discussing is there, but it cannot be found at 

 present: let us pass on." And no wonder, if we consider that 

 even so low a magnification as 100 diameters will offer in an ob- 

 ect 1 centimeter in diameter 70 to 80 fields, while a power of 

 600 will furnish 1500 to 2000 fields, and if the object sought for 

 in a power of 600 measures 1 millimeter in diameter it v;ill be 

 1-30,442,478 of the whole. It is sufficiently clear, therefore, 

 that such a search can be successful only by mere accident or 

 as a result of long and patient parallel motion of the slide. 



I have had my share of these vexations. To overcome 

 these difficulties and to add to the usefulness of the microscope, 

 I submit this little contrivance. It is as simple as I hope it 

 will be practical. Its object is twofold; first, to bring every part 

 of the section, by the shortest route once under the microscope 



