A very great amount of scientific effort has been expended in the last few years on Rocket research and development. This work has been carried out in many countries besides Great Britain, notably the U.S.A., Germany and Russia. In the main it has been done by government scientists or by firms and universities under government contract. This is understandable since the chief use of rockets so far has been a military one. There is a very long history of the use of rockets in warfare (they were used at Waterloo), culminating in the production and firing of the German V2. Most of the major rocket weapons produced in the last war have been described in general terms in the Press, but there is, at present, remarkably little mathematical or scientific literature on the subject. Various technical journals,e.g. Flight, have published articles on the various aspects of the rocket problem, and there are one or two books. This lack is due to the fact that most of the papers written during the war years are classified as Secret or Confidential and are not yet available for open publication. Two recent papers are worthy of mention : one by Perring (1) on German Long Range Rocket Development, which gives a considerable amount of data on the V2 and one by Malina and Summerfield (2) on Rocket Escape from the Earth which discusses the possibilities of very large rockets. These may be regarded as the forerunners of very many papers which should eventually find their way into scientific literature.

In these days of examinations and syllabuses it is perhaps not superfluous to remind teachers of the maxim that they ought to teach more than their pupils need to learn. To be an expert on circles it is necessary to study other conics, and to appreciate homographies it is as well to know something about other correspondences.

The ideas of correspondence and characteristics of systems of conics are due to the French mathematician Chasles (c. 1850) and a large collection of illustrations of these subjects may be found in T. Lemoyne's Les Lieux Géométriques (Vuibert, 1923). These illustrations include, though in a summary form, the subject of the present article. Reference may also be made to the last example in C. Taylor's Ancient und Modern Geometry of Conics, and to a note in Salmon's Conic Sections.

If, like David Copperfield, you are on the road to Dover, for the first time and with no one to guide you, and you come to a point where the road forks, then of all your mathematical knowledge, only the method of reductio ad absurdum can help you. For if you choose the wrong turning, and find yourself in Folkestone, you may be quite sure you ought to have taken the other road.