A load is attached to the axle of a sheave and the whole suspended by means o'f a rope passed around the sheave so as to divide the load on the rope into two parts. Call that part of the rope on one side of the sheave A and that on the other side B. The suspended load amounts to 40,000 pounds. With the end of the rope B fixed, what will be the pull at A necessary tp lift the load if friction reudces the efficiency to 97.5 per cent. What will be the pull at B ? Solution by S. E. Guffin. Let x ==

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... pull on A. Let y == pull on B. x-}-y = 40,000 pounds. y === .975^. x = 40,0000 .975;r. 1.9^'5/r = 40,000. x == 30,253 pounds. y = 19,747 pounds. Solution by S. ,/7. Atwood, Dayton, Wash. The mechanical advantage of this arrangement is 2. Hence the theoretical effort required at A is 20,000 pounds, but, since the efficiency of the system is only 9'7.,5 per cent, 20,000 .975 = 20,513 pounds, total pull at A. The pull on B = 40,000 20,513 + the amount due to friction in /the pulley. [Why are the results different .and which is correct?] Mr. Atwood says: "I think the difference in results between Mr. Guffin and myself is due to a different interpretation of efficiency. My conception of efficiency is the ratio of the total load to the effort and not the ratio between the pulls on the two cords." [The following was sent in answer to Question 86 of this department. Ed.] Why give a laboratory examination similar to that given by Harvard University? What can an examiner find out by such an examination? In what ways can the examination benefit (1) the pupil; (2) the teacher? In ans'wer to your inquiry concerning the merits of the Harvard laboratory admission examinations in science, we. as three members of the Department of Physics who have had experience in these examinations, make the following statement of the matter as it appears to us: There is a very strong family resemblance among all the physics laboratory notebooks from any one school, so that a laboratory test is almost necessary to show which candidates have done the experiments mtelli-