21 



frame, and apply another drop of the shellac to the opposite cut with its enclosed 

 web. Wait several minutes before cutting off the two ends of the web, and then 

 proceed in the same manner with the web which is to be placed at right angles to 

 this one. 



NOTE. The fine spider-threads used were formerly taken from the cocoons of the small black wood-spider; 

 now, however, we obtain them from the cocoons of a species of spider found in Michigan. These threads are 

 }ue, and not apt to relax their tightness if properly placed on the diaphragm, and as they retain theii 



elasticity, they are preferable to platinum wires, which have a tendency to break, owing, to their great brittle- 

 ness. The best spider-threads are those of which the spider makes its nest. These nests are yellowish-brown 

 balls, which may be found hanging on shrubs, etc. , in the late fall or early winter. The nest should be torn open and 

 the eggs removed ; if this is not done, the young spiders, when hatched, will eat the threads. The fibers next to the 

 eggs are to be preferred on account of their fineness and darker color. As it is important to get the proper kind 

 of spider-web, we subjoin an extract from a letter addressed to us on the subject by Prof. J. B. Davis, Uni- 

 versity of Michigan, Ann Arbor, Mich., to whom we are indebted for our supply. 



" The species of spider of which I send you cocoons is not difficult to find in Ann Arbor Lat. 42 z(S N. 

 as far as my experience goes, and is numerous on Beaver Island, out in Lake Michigan about 46 N. at 

 St. James. I have also always succeeded in hunting it in our Michigan woods, in places of concealment, under 

 bark of dead trees, in cracks and holes, about old stumps, logs, and the like. It is especially partial to painted 

 woodwork. It roosts high, the higher the gable the more numerous the cocoons ; but it is also found on fences 



either, and many persons in my observation have had them freely crawling over their hands, face and body. 

 They may be certainly gently handled without the least harm. They both (male and female) bear a plain 

 escutcheon design on the back of the abdomen; female much the more beautiful, in browns. Colors all 

 brown and yellowish brown. The cocoon is a snarl of webs, and is attached under ledges of window-sills, cor- 

 nices, projections of gables, and the like partly sheltered places. The color of the threads you have is of a light 

 corn-color, distinctly separating it from the white cotton-like cocoons so common everywhere. The threads are 

 silky, not like cotton. Of late years I keep one or two nice cocoons where they can be reached. You know one 

 can wrap them in a bit of paper and carry them in the pocket, or any such place, and they ara always ready." 



Prevention Better than Cure. 



IT cannot be denied that instruments frequently meet with serious accidents 

 which, with a little care on the part of the operator, could be prevented. It cer- 

 tainly does not betoken proper care to leave it standing unguarded in a street, road, 

 or pasture, or in close vicinity to blasting, or to expose it unnecessarily to the burning 

 rays of the sun, or to dust, dampness, or rain at any time. Such carelessness must 

 inevitably result in deterioration of the accuracy and efficiency, not to speak of the 

 durability, of an instrument. 



It should be borne in mind that there are many parts of an instrument which, ij 

 once impaired, cannot be restored to their original efficiency ; and when it is consid- 

 ered that a conscientious maker bestows no little care, time, and expense on his 

 work in order to attain a high degree of perfection, such neglect seems like a 

 wanton waste of human energy and skill. 



Legs of tripods, if fitting too loose or too tight, and dull shoes are frequent 

 sources of falls, and loose shoes tend to make an unsteady instrument. The test 

 of the proper degree of the tightness of the legs is this, that if the leg is raised to a 

 horizontal position and left free, it should gradually sink to the ground. If it drops 

 abruptly it is too loose ; if it does not sink it is too tight. 



When taking an instrument from its box, it is not immaterial where and how to 

 take hold of it. To lift it by the telescope, circles, standards, or wyes is improper, 

 ,nd while it may not be attended at "once with any serious consequences, yet it may 

 sometimes lead to some permanent injury, and it certainly is always fraught with 

 danger to the permanency of the adjustments. In handling, it is always best to 

 place the hand beneath the leveling base. 



When mounting an instrument on the screw of its tripod, or screwing any of its 

 parts together, it is important to turn the part in the direction of unscrewing until it 

 is perceived by a slight jar that the threads have come to the point where they en- 

 ter ; the motion may then be reversed, and the parts screwed together. 



To secure an even wear of tangent and micrometer screws, they should be used 

 -equally on all portions of their lengths. 



