100 YEARS AGO

The Fourth Dimension. By C. Howard Hinton, M.A. A book bearing the present title may be reasonably expected to contain certain things. In the first place it should have a clear exposition of Descartes's applications of algebra to geometry, and conversely of geometry to algebra, the logical conclusion of which consists in the removal of all restrictions as to the conceivable number of dimensions of space. In the second place it should contain clear, concise, and exactly worded statements of the peculiar and distinctive geometrical properties which are characteristic of spaces of two, three, four, or more dimensions respectively... Now such things as these are either entirely absent from the book or else they are mixed up with such a mass of irrelevant and discursive matter as to render it often quite impossible to make out what the author is driving at... There is a certain class of individual, far too common in this country, who busies himself in pestering his mathematical friends with long and rambling letters on such questions as “What is the fourth dimension?” or “What is the ether?” Such people very rarely know anything about the three dimensions of the space they live in, but Mr. Hinton's book will, it is to be hoped, give them something to think about which will at least amuse them and keep them occupied.

From Nature 21 July 1904.

50 YEARS AGO

It is firmly believed by most theoretical physicists that the antiparticle to a proton can exist... This particle should bear the same relation to a proton as does the positron to an electron. Should it be possible to create such a particle by a proton–nucleon collision, the incident proton will require a kinetic energy of at least 5.6 × 109 electron volts. At present only one particle accelerator, the Berkeley ‘Bevatron’, exists which is designed to reach this energy. At this energy the production of antiprotons is not expected to be very copious, and their abundance relative to other particles formed will probably be far smaller than in many cosmic ray phenomena which have already been extensively investigated. The problem of the conclusive identification of the antiproton may be a difficult one for some time to come.

From Nature 24 July 1954.