26 THE AMERICAN MONTHLY [February, 



for receiving central stops and blue glass. This is, unquestionably, the 

 most perfect mounting for controlling substage illumination. 



It can be attached to an adjustable substage or to a substage fixed 

 to the stage, and may be used with the high and low-angled Abbe con- 

 denser. 



A Microscope Stand.* 



By T. J. BuRRiLL, Ph. D., 



CHAMPAIGN, ILL 



It is proposed to describe an instrument for general, practical work, 

 for student and investigator, with nothing which can be omitted with- 

 out detriment, and with no more expense than barely sufficient for the 

 best accomplishment. 



Of course, it will be understood that this is from the standpoint of a 

 microscopist rather than that of a mechanician. 



The foot must stand upon three points, and these should be shod 

 with rubber. With the centre of gravity adjusted for it, the two pro- 

 jections are best directed backward, to prevent easy tipping when the 

 tube is inclined. This disposes at once of the horseshoe base so gen- 

 erally used in confinental Europe. In fact, the dismissal is too uncer- 

 emonious, for whh the small and short tube used on these instruments, 

 and with the amount of metal in the foot, the danger mentioned is 

 practically obviated. But it seems to me that the extra weight of the 

 base is a cumbersome makeshift which ought to be avoided if practi- 

 cable. In regard to the small tube,, something will hereafter be said. 

 As a further security of the instrument from tipping obliquely, side- 

 wise, and backward, the hind resting-point of the horseshoe-base is 

 usually considerably extended sidewise. An excellent German stand, 

 the most popular one in the country, has this rest one and seven-eighths 

 inches wide, thus practically making four points in contact with the 

 table — another fault in construction. But for an upright instrument, made 

 as low as possible, with its centre of gravity well down towards the table, 

 it is, after all, the best form. It allows the mirror to swing down to 

 the table itself, and, with the conditions stated, the stand is sufficiently 

 stable. Stability depends more upon the poise of the instrument than 

 upon the weight of the foot. A heavy foot is of no advantage, aside 

 from keeping the instrument from falling over, if other things are prop- 

 erly made. With rubber rests a very light stand does not easily slip on 

 the"^ smoothest surface, and such rests do vastly better service than sev- 

 eral pounds of metal in preventing tremor communications. 



In my ideal instrument I should, therefore, have a tripod base, with 

 the single projection forward, and this flat and thin, so as not to seri- 

 ouslv interfere with substage room, the whole simply heavy enough 

 and broad enough for reasonable security, the weight being considera- 

 ble less than half that usually put into the horseshoe form. There 

 should be two supporting pillars rather than one, both for good appear- 

 ance and the tendency to greater firmness, coupled with ease of move- 

 ment of the compound body. This last should be easily regulated by 

 a screw to control the friction. A stop should be provided by which 

 the instrument may be accurately brought to the horizontal. 



*Abstracted from the Proceedings of the American Society of Microscopists, volume xi. 



