Journal of Applied Microscopy. 



Ill 



appropriations made for apparatus, are 

 the general requirements. 



In conformity with this tendency, 1 

 have endeavored to construct an instru- 

 ment which shall fulfill these conditions 

 and still be a scientific instrument and 

 not a toy, a problem rather more 

 difficult of solution than might be 

 supposed. 



A choice must be made between two 

 types of instruments, one having the 

 coarse and fine adjustment by means of 

 a good rack and pinion, the other hav- 

 ing a sliding-tube coarse adjustment and 

 fine adjustment by micrometer screw. I 

 designed an instrument corresponding 

 to the first form last year for the exam- 

 ination of meats and other food stuffs, 

 and a description of the second form is 

 the purpose of this paper. 



The qualities of a perfect fine adjust- 

 ment are delicacy, rigidity, and perma- 

 nency. The form of construction now 

 followed in the continental types of 

 microscopes is generally accepted as the 

 best, but its use in any simple instrument 

 is precluded on account of its considera- 

 ble cost. I have succeeded in devising 

 a form of fine adjustment which has 

 proven an excellent substitute. The 

 instrument to which I have applied it 

 has a small japanned iron base, the 

 pillar and arm is a single brass rod, 

 seven-eighths of an inch in diameter, in 

 the upper half of which is recessed a 

 V-way with a T cross-cut to which the 

 arm is fitted. This combines extreme 

 rigidity with compactness. Recessed 

 into the lower end of the pillar is a 

 spring which forces the arm upward 

 against a micrometer screw which is 

 attached to the upper extremity of the 

 rod. In the lower end of the screw a 

 hardened steel pin is recessed so that 

 eccentricity of the screw cannot possibly 

 be conveyed to the arm. Attached to 

 th arm is a plate which receives the 

 sleeve tube in which the body tube car- 

 rying the eyepiece and objective slides. 

 The body tube is of standard size and 

 of a fixed length of 160.0 mm. The stage 

 is fastened to the pillar rigidly, is of 

 liberal proportions, and is provided with 

 a revolving diaphragm. The dimensions 

 of the instrument are as follows: Total 

 length with objective and eyepieces 

 attached ready for use, 11 inches; stage, 

 3i by 31 inches. The outside dimensions 

 of the case are 11 inches high, 4J inches 

 wide, 5h inches deep. The portability 

 and permanent working qualities of this 

 instrument make it an ideal travelling 

 microscope, while its simplicity of con- 

 struction, and the fact that it possesses 

 a good working coarse and fine adjust- 

 ment fit it for school use. 



Edward Bausch. 



Rochester, N. T., June 10, 1898. 



Hints on the Construction of a 

 Tow Net. 



A tow net for the collection of pelagic 

 organisms is an essential part of the 

 equipment of the biological laboratory, 

 yet few possess one of the most conven- 

 ient and practical forms. Such a net 

 serves as the most effective and rapid 



Fig. 1. 



method of collecting the pelagic life of 

 marine and fresh water, and is conven- 

 iently operated by drawing it behind a 

 boat, or by lowering it to the desired 

 depth and then drawing it to the sur- 

 face of the water. The organisms in the 

 water of shallow pools or in the midst 

 of vegetation may be secured by pump- 

 ing or dipping the water into the net. 

 In salt water the tow net secures the 

 pelagic algae and diatoms, the adult 

 pelagic invertebrates, and the larval 

 stages of many others, and also the eg-js 

 and fry of many fish. In fresh water the 

 catch usually consists of Entomostraca, 

 Rotifera, Protozoa, Diatoms, Desmids, 

 the smaller algae, and a few insect lar- 

 vae. Even Hydra may at times be taken 

 in quantity in the deeper wateis of shal- 

 low ponds and lakes in the spring and 

 early summer, when the plankton is 

 abundant. 



