Mar. 2, 1 888.] 



SCIENTIFIC NEW^S. 



213 



JUNIOR ENGINEERING SOCIETY. 

 On the 3rd inst. a paper was read before this Society on 

 "Some Novel Mechanisms " by Mr. W. J. Tennant, who 

 pointed out that the most curious and complex forms of 

 mechanisms were but combinations ot the simple me- 

 chanical powers. As an example of the lever the oar 

 was mentioned, and the controversy as to the correct 

 position of its fulcrum was alluded to. In reference to 

 novel gearing, Watt's sun and planet and annular motions 

 were described, as was also Ferguson's paradox, and 

 Heinrich's improvement upon it. General Cameron's 

 device for transmitting motion by shafts whose axes are 

 at an angle with each other without varying the angular 

 velocity of the driven shaft was explained. The paper 

 concluded with an extended description of Professor 

 Hele Shaw's sphere and roller mechanism for varying 

 velocity ratio without introducing sliding friction. 



LIVERPOOL MICROSCOPICAL SOCIETY. 

 At the meeting held on the 3rd February, Mr. A. Norman 

 Tate, F.I.C., F.C.S., in the chair, Dr. Frederick C. 

 Larkin read a paper " On Making Permanent Microsco- 

 pical Specimens of Blood," in which he described in 

 detail the methods most suitable for mounting specimens 

 of the blood of different animals. Mr. Willoughby 

 Gardner then read a paper on "Wing Scales of Butterflies," 

 in which he described the many beautiful forms and 

 colours of the scales, and the usual modes of arrangement. 



LIVERPOOL BIOLOGICAL SOCIETY. 

 At the meeting held on the nth inst., the first part of an 

 elaborate paper upon the minute anatomy of limax, the 

 common slug, was brought before the meeting by Dr. R. 

 Hanitsch. This was followed by a short paper on " The 

 Alternation of Generations and Specific Nomenclature in 

 Salpa and other Animals," by Professor Herdman, D.Sc. 



THE VICTORIA INSTITUTE. 

 At a meeting held on the 6th inst., a paper upon the 

 " Order of Creation " was read by Professor Warring, 

 of Ploughkeepsie, in which he reviewed recent scientific 

 statements, and compared the results of the investigations 

 of Sir W. Dawson, Professors Dana, Huxley, Asa Grey, 

 Agassiz, and others. 



CORRESPONDENCE. 



The Editor does not hold himself resfonsible for opinions expressed 

 by his correspondents, nor can he take notice of anonymous com- 

 munications. All letters must be accompanied by the name and 

 address of the writer, not necessarily for publication, but as a 

 guarantee of good faith. 



WHAT KIND OF LEVER IS AN OAR? 

 I have been accustemed to consider that the action of an 

 oar in a boat is m accordance with a lever of the second kind, 

 that is, where the fulcrum is at one end, the power at the 

 other, and the resistance between the two. The text-books 

 on mechanics point out that the fulcrum is in the water, and 

 the resistance acts at the rowlock. Now in reading a paper 

 in the Philosophical Magazine (January, 1887), I was 

 astonished to see that the writer of the paper — the Rev. T. 

 K. Abbott — makes the true fulcrum to be at the rowlock, and 

 that the oar belongs to the levers of the first class. He 

 considers that, according to the orthodox theory, it would 

 follow that the power would have the advantage over the 



resistance in the proportion of about 4 to 3 (this being 

 usually about the proportion of the whole length of the oar 

 to the part outside of the rowlock), and that if the rower's 

 hand is moved nearer to the rowlock the mechanical advan- 

 tage would be slightly diminished. Now if the oar were a 

 lever of the first kind, the second conclusion would be 

 still true, but there would be a mechanical disadvantage of i 

 to 3 in using the oar, in point of power to be compensated 

 for by some gain in speed. 



Fig. I. 



Fig. 2. 



Vf 



A 



According to our text-books, Fig. i represents the action ot 

 the oar ; and, according to Mr. Abbott, fig. 2 represents this 

 action. Of course he must assume as I assume, that the 

 boat is to be moved by two oars on which equal pulls are 

 executed, and which are perfectly symmetrical on both sides. 

 Let P be the half pull of the rower or rowers, R the semi- 

 resistance of the water to the motion of the boat, or the 

 semi-reaction\between the oar and the boat at the rowlock. 

 The oar at F (its blade) is pressed against the water by the 

 rower, and as action and reaction are equal and opposite, the 

 water makes a corresponding resistance to the blade ; at each 

 blade let this semi-resistance be called S. Then in Fig. I 

 P X 4 = R X 3, and R = P + S .-. S = J P. If, according 

 to Mr. Abbott, what I call S he assumes to be the semi- 

 resistance of the water to the motion of the boat, then P x i 

 = 8x3, and S = T P' But if with him as with me, R is the 

 semi-resistance of the water, then P x i = R x 3, and R = ^^ 

 P, whereas with me R = | P. He does not make it clearer 

 by stating : — " Suppose the rower to be in the boat as usual, 

 but the boat to be fixed, while the oar presses against another 

 boat which is free to move. Iti thiscase the oaris manifestly 

 a lever of the first order ; but the relative position and 

 action of the oar, the power, and the resistance are in every 

 respect precisely the same as in ordinary rowing." Because 

 in this case the rowlock would undoubtedly be the fixed 

 fulcrum, the hand the moving power at one end of the lever, 

 and the other boat the movable resistance at the other end. 

 That, however, alters the whole question. It changes the 

 lever from one of the second kind to the first, the power is 

 exercised to move another boat in the opposite direction of 

 the hand. Now as it is a very important difference to say 

 with the common theory that (in the case specified) the 

 power exerted is J of the resistance, and with this new theory 

 that the power exerted must be three times the resistance, I 

 would like to know the opinion of any of your readers on the 

 subject. — Athletic. 



QUESTIONS IN ASTRONOMY. 

 Will you or any of your astronomical readers give me the 

 mean time of full moon on the 28th January, and the mean 

 anomalies of the sun and moon, according to the lunar tables 

 used by astronomers of the present day ; and also the sun's 

 mean distance from the Node. I only possess Ferguson's 

 tables, which come down no lower than 1800; and I do not 

 know whose tables are now used, but desire to test my cal- 

 culations of the eclipse. J. de D. 



THE COLOURATION OF BUTTERt LIES. 

 Is the following, which I quote from a back number of the 

 Revue Scientifiq}<e correct '^■. — "Mr. Nicholas Wagner, using 

 an exceedingly sensitive galvanometer, has discovered fixed 

 currents in the wings of butterflies, and with the aid of electric 

 currents has succeeded in producing changes in the nature 

 and arrangement of pigments." A Coloorist, 



