We are thrown back, then, on such experiments as may be provided for us by the uncalculated operations of man through many ages. This class I call undesigned experiments and have had more to say about numerous examples of these in another place.[57] Using the term experiment broadly we see many occurrences which consist in an accidental observation of a fact, and Jevons mentions five of these which have led to organised results in science--the double refraction in Iceland spar by Erasmus Bartholinus, the twitching of a frog’s leg under stimuli by Galvani, the light reflected from distant windows with a double-refracting substance by Malus, the form of a vertebra by Oken, and the peculiar appearance of a solution of quinine by Sir John Herschel. But he notes something further than this, that is, the way in which astronomers make the earth’s orbit the basis of a well-arranged _natural experiment_. He says further that “Nature has made no experiment at all for us within historical times” among animals living in a state of nature, allowing at the same time that man has made an approach to experiment in his domestication of many animals. Huxley himself kept an open mind until the last as to the validity of Natural Selection in the Origin of Species, because of the fact that races which are sterile together have not yet been produced by human cultivation, for example, the sterility of mules, the human product of the jackass and the mare. I allude to this to show that such a result, if effected, would have constituted a valuable experiment in biology in favour of Natural Selection. [57] _Contemporary Review_, June 1917. Harness on Horses. Man has, however, been carrying on unconsciously throughout a great stretch of time an experiment upon the hair on the coat of a horse by the use of harness. This is an old story and its rudiments are mentioned by Professor Scott Elliott.[58] He states that the men of Cromagnon are believed by a high authority as to their rock-paintings to have depicted some marks which represent rude harness of some kind, though he himself expresses doubt on the matter. He also quotes the same authority for the figures made by the Madelenians as having found signs which can be interpreted as halters or even bridles. Be this as it may, we need not carry our search for the use of harness to this hoary antiquity, but know well from history that for many thousands of years man has been employing harness on his friend and servant, thus making the essential conditions for an experiment of which he and his servant were alike unconscious, that is to say, he influenced a growing living structure, the horse’s hair, by the artificial force of pressure, applied to the coat at various points. These varied from age to age as to fashion and material, and the present full development of harness of a draught horse was probably slow in coming. [58] _Prehistoric Man and His Story._ G. F. Scott Elliott, 1916, pp. 169, 206.