158 THE AMERICAN MONTHLY [July, 



and the more perfect and satisfactory it will be. In considering the 

 various parts of the stand, the above illustration of the Griffith 

 Club Microscope will serve to make them clear : 



The base^ or lower portion of the stand, first attracts our attention. 

 Instruments can be found with bases of almost all conceivable forms, 

 but the only one suitable for druggists is the tripod. 



They<?<?/ forming the tripod may be disguised in the form of the base ; 

 but that does not matter, so long as there are three, and only three, 

 points of support; This not only gives the greatest. stability to the in- 

 strument, with the least tendency to vibrate when the table is jarred, 

 but also has other advantages. One of these feet should always point 

 toward the observer. This is of importance to the pharmacist, who 

 has frequent occasion to incline the instrument while measuring or 

 drawing objects by means of the camera lucida. The only exception 

 to this is when the tripod has two long feet, as shown in the extra foot 

 of the above illustration. In such a case it is justifiable to have the 

 short foot directed from the observer. 



The pillar^ or s?ipport^ requires no special attention. With some 

 instruments it is single, while others have a double support, so that the 

 mirror bar swings between them. Pharmacists are not especiallv in- 

 terested in either of them. 



'Y\\Q. joint seen at the upper end of the pillar is a feature of more im- 

 portance, and every pharmacist should see that his instrument can be 

 inclined to any desired angle. If it is required that the instrument be 

 used upright, it can be so employed just as well as the stift-backed ones 

 that we still see in the market. However, it is seldom that a druggist 

 has occasion to use an instrument in that awkward position. This 

 joint is usually a single hinge, but it may be secured by means of 

 trunnions, and in such cases is usually provided with some means of 

 tightening or loosening the bearings. Some instruments can be locked 

 with the body at any desirable angle. This, however, is not necessary 

 for a pharmacist's use. 



The arm is not very prominent in our illustration. It is the portion 

 above the joint, and bears the body. In some instruments it is promi- 

 nent and closely resembles in form the flexed human arm. If it supports 

 the body firmly, that is all that is required. 



The body is supported by the arm, and has attached directly to it 

 the optical parts of the compound microscope. The body varies in 

 size and length in different instruments. The size is not of very much 

 importance, but in length it should be what is known as " standard," 

 or be so arranged that it can be lengthened out. The body must be 

 perfectly black inside, and this is best accomplished by means of black , 

 cloth. Cloth is more permanent than the blackened metal surface. 



The draw tube is found only in the better class of instruments, and 

 is a provision for adjusting the length of the body. With very high 

 power objectives it is very essential to have a draw tube. It should be 

 marked to indicate when the body is '" standard " length. A great con- 

 venience is a " society screw " in the lower end of the draw tube. 

 Pharmacists have frequent occasion to use quite low powers, and if the 

 low power objective is placed in the draw^ tube there will be plenty of 

 working distance, which I have found is not the case with some instru- 

 ments. Again, it enables the pharmacist to place the analyzer of the 



