544 



REPORT 1886. 



radius SO describe the circle AKL, cutting in K, L any other pair of rectan- 

 gular axes OK, OL which pass through 0. Then PK, QK are the radii of 

 gyration about OK, OL respectively, and twice the area of the triangle PKQ is 

 the product of inertia about them. In particular, if PQ be 

 produced to cut the circle in D and E, the principal axes at 

 O are OD, OE. 



If I is the centre of inertia, di-aw OK passing through I, and 

 draw IM perpendicular to 01 and parallel to OL. Then the 

 product of inertia about IK, IM is equal to that about OK, OL, 

 and is therefore known ; the radius of gyration about OK is 

 known, and that about IM is also known, as its square is less 

 than that of the radius about OL by the square of 01. Hence 

 the principal axes at I can be found by a fresh application of the above con- 

 struction or by the construction given below. 



11. OX, OY are the given axes, OA. the product of 

 inertia about them, AP the moment of inertia about OX, 

 AQ that about OY, PAQ being in a line parallel to OY, 

 and as drawn in the figure. Bisect PQ in S, with centre 

 S and radius SO describe a circle. If OK, OL are an- 

 other pair of rectangular axes, and K the point where 

 OK cuts the circle, then if KM be drawn perpendicular 

 to PQ, PM, QM are the moments of inertia about OK, 

 OL respectively, and KjM is the product of inertia about 

 them. If PQ cuts the cu'cle in D, E, the principal axes 

 at are OD, OE. 



+X 



TUESDAY, SEPTEMBER 7. 



The following Reports and Papers were read : — 



Report of the Committee for reducing and tahtdating Tidal Observations 

 in the English Channel, made ivith the Dover Tide-gauge, aiul for connect- 

 ing them with Observations made on the French Coast. — See Reports, 

 p. 151. __^__ 



RepoH of the Committee for constructing and issuing practical Standards 

 for use in Electrical Measurements. — See Reports, p. 145. 



3. Report of the Committee on Electrolysis. — See Reports, p. 308. 



4. On an Electric Motor Phenomenon.^ By "W. M. Mobdet. 



When testing an electric motor in the works of the Anglo-American Brush 

 Electric Light Coi-poration a phenomenon presented itself which the author at 

 first found some difficulty in explaining. The motor was of the Schuckert-Mordey 

 ' Victoria ' type, series-wound, constructed to give 36 horse-power with a current 

 of 20 amperes. It was supplied with power by a large Brush dynamo. On starting the 

 generator on the occasion in question, the motor, being connected in the circuit, also 

 started, but ran very slowly, and developed but little power. There being 

 apparently some fault in the connections or elsewhere, the circuit was opened in 

 order to stop the motor for the purpose of examination. On breaking the circuit 

 the motor, which at the time was running slowly, stopped suddenly, and instantly 

 started again, running backwards or oppositely to its usual directioDj at a rate of 



' This paper was published m extenso in the Electrical Review, vol. xix. p. 259 

 (Sept. 10, 1886), and in other journals. 



