28 THE ART OF PROJECTING. 



the object, it will be seen that some of the light does 

 not pass through it. If the object d be moved toward 

 the objective, then some parts of it will not be lighted, 

 and consequently but a part of it would be projected. 

 If the object d is quite small, like a fly, or a flea, or a 

 small crystal, it will be necessary to bring it forward, 

 toward the focus of the condenser, where it will be 

 more strongly lighted, and allow the use of an objective 

 of shorter focus, and consequently higher magnifying 

 power. If the object be made of wood, or any kind of 

 tissue, be careful about bringing it very near to the 

 focus, as the great heat there may destroy it in a few 

 seconds. This danger may be somewhat lessened by 

 placing between the condenser and the object the chem- 

 ical tank, containing a strong solution of alum. The 

 common pocket botanical glass, having a focus of an 

 inch or two, will answer for very much of this work, 

 but Zentmayer's inch-and-a-half gas microscope object- 

 ive is superior to any other lens I have seen for such 

 projections. 



This arrangement is essentially the solar microscope. 

 The object may be exceedingly minute if the objective 

 has a very short focus, say half an inch, or less. 



It is possible to magnify an object a thousand diam- 

 eters, or a million times, and still have it so well lighted 

 that a large audience can see it plainly. A list of 

 things that are suitable for projections with this ar- 

 rangement is appended, mainly for the purpose of indi- 

 cating the breadth of its field of usefulness : 



Hairs of various animals, which may be held between 

 two strips of glass. Down from the wings of moths and 

 butterflies ; these will adhere to a piece of glass with- 

 out any pressure. Scales of fishes. Eyes, legs, and 

 wings of flies, or the whole of any insect. Stings of 



