464 Intelligence and Miscellaneous Articles. 



of Spheres, Cones, Cylinders, and Pyramids, together with the 

 _" development " of the surfaces of the two last-named solids, — refer- 

 ence being made for other cases to the " Cry stall ography " of the 

 Series — contain what is regarded as the more elementary portion 

 of the subject. More advanced problems on the Line and Plane : 

 on the Projections and Plane Sections of Solids : on the less easy 

 determination of the Intersections of Solids, as exemplified by two 

 simple cases : on the Determination of Tangent Planes to Cylinders, 

 Cones, and Spheres : on the Projection of Shadows : on Isometric 

 Projection, cursorily treated, and stated to be " a branch of Ortho- 

 graphic," which latter adjective is barely explained as " G. oi*ihos, 

 right, straight; grapho, I write" — for "draw: "the six cases of 

 the Spherical Triangle: lastly, on "Horizontal Projection." 



It would be unreasonable to expect that so extensive a pro- 

 gramme could be treated with an adequate amount of demonstration 

 within the limits prescribed to the author. Student-life is short ; 

 and it is deemed necessary to train a certain number of proficients 

 in the correct performance of the constructions, whether " the 

 reason why " is known or not : " Est quadam prodire tenus, si non 

 datur ultra." The diagrams inserted amidst the text are copious 

 and generally clear ; while each chapter is accompauied by a 

 number of examples for exercise. 



The second part of the volume of 48 pages, numbered anew, 

 gives solutions of the most elementary problems of Constructive 

 Geometry (pp. 1-10) : the constructive performance of the four 

 rules of Arithmetic, of im^olution and extraction of square roots 

 (12 pp.): the representation of areas and volumes by straight 

 lines (15 pp.) : the elementary parts of " Graphical Statics " as far 

 as the Equilibrium of Coplanar Forces and the determination of 

 Centres of Gravity of Plane Areas : finally, a selection of Exercises 

 taken from the Science Examination Papers " with hints and 

 solutions " (21 pp.) — a section requiring careful revision. J. J. W. 



XLIX. Intelligence and Miscellaneous Articles. 



ON THE STRENGTH OF THE ELECTEICAL WAVES WHEN THE 

 SPAEK PASSES IN OIL. BY H. BAUEBNBEBGEE. 



rpHE author pursues the experiment of Sarassin and De la Rive 

 -*- and shows by quantitative measurement how in Lester's ar- 

 rangement the electric resonance is increased if the primary spark 

 passes in oil instead of in air. The investigation of different 

 oils shows that petroleum gives the best results not only as regards 

 the strength of the resonance, but chiefly because in it the change 

 in the electrodes and the dielectric is least. In the preliminary 

 experiments the influence of the capacity of the electrometer used 

 in the measurements is investigated, and the author finds that in 

 comparative measurements the changes in capacity of the electro- 

 meter have no influence on the changes of capacity, but that for 

 each distance of the electrodes a definite current-strength is re- 

 quired to produce a maximum of electrical resonance. In con- 

 clusion it is shown that the length of the conducting wires to the 

 primary condenser is of little influence. — Wien. Ber., July 13, 1893. 



