Hence Fresnel's hypothesis as to the behaviour of ether inside matter is equivalent to the assumption that a potential function, ∫ μ² v cos θ ds , exists throughout all transparent space, so far as motion of ether alone is concerned. Given that condition, no first-order interference effect due to drift can be obtained from stationary matter by sending rays round any kind of closed contour; nor can the path of a ray be altered by etherial drift through any stationary matter. Hence filling a telescope tube with water cannot modify the observed amount of stellar aberration. The equation to a ray in transparent matter moving with velocity _u_ in a direction φ, and subject to an independent ether drift of speed _v_ in direction θ, is ∫ ds / (V/μ cos ε + v/μ² cos θ + u[1 - (1/μ²)] cos φ) = const. WILLIAM BRENDON AND SON, LTD. PRINTERS, PLYMOUTH Science for the General Reader WORLDS IN THE MAKING The Evolution of the Universe. SVANTE ARRHENIUS, of the Nobel Institute, Stockholm. Illustrated. 6_s._ net Explains the origin of nebulæ from suns and suns from nebulæ, the universal distribution of life, the conservation of energy, etc., and shows how all may be accounted for by the newly developed principle of the pressure of light ASTRONOMY WITH THE NAKED EYE G.P. SERVISS. Illustrated. 6_s._ net Telling all that may be seen in the skies without the aid of the telescope THE FRIENDLY STARS M.E. MARTIN. Illustrated. 5_s._ net A handy volume, enabling the reader to identify the principal stars and constellations SIDELIGHTS ON ASTRONOMY Prof. SIMON NEWCOMB. Illustrated. 7_s._ 6_d._ net Discusses such topics as "Are the Planets Inhabited?" etc. etc. THE CHEMISTRY OF COMMERCE Prof. R.K. DUNCAN, author of "The New Knowledge." Illustrated. 7_s._ 6_d._ net; post-free, 7_s._ 11_d._ An account of the scientific processes involved in modern industry, with valuable suggestions for their extension NEW CONCEPTIONS IN SCIENCE CARL SNYDER. Illustrated. 7_s._ 6_d._ net Dealing with the new worlds revealed by the microscope, telescope, etc., and the latest scientific theories based thereon NINETEENTH CENTURY SCIENCE Dr. HENRY SMITH WILLIAMS. Illustrated. 9_s._ A review of the great scientific achievements of modern times, and the problems now being investigated "Short studies on great subjects by distinguished living men."--_The Standard._ HARPER'S LIBRARY OF LIVING THOUGHT _Foolscap 8vo, gilt tops, decorative covers, richly gilt backs Per Volume: Cloth 2s. 6d. net, Leather 3s. 6d. net_ Some Contributors: ALGERNON CHARLES SWINBURNE COUNT LEO TOLSTOY W.M. FLINDERS PETRIE SIR OLIVER LODGE THEODORE WATTS-DUNTON SVANTE ARRHENIUS ERNEST A. GARDNER ARNOLD MEYER SIR WILLIAM CROOKES &c. &c. "A permanently useful addition to literature."--_The Daily Telegraph._ "Presenting suggestive 'living' thoughts on subjects of vital interest."--_The Times_