Accident has played a noteworthy part in both discovery and invention. Nathaniel Hayward long ago remarked that sulphur deprives rubber of stickiness. Charles Goodyear one day combined some rubber and sulphur by way of experiment; quite by accident he overturned part of the mixture upon a hot stove. He saw in a moment that heat is essential to make rubber insensible to both heat and cold: he had indeed discovered vulcanization. Examples of this kind abound in the history of every art. As far afield as the war on insect pests in France a priceless discovery was hit upon unsought a few years ago. One autumn the vines were still suffering from phylloxera when a mildew caused by a fungus began to do serious damage to crops. Through the spraying of vines with blue-stone to prevent pilfering of fruit, it was noticed that the fungus was killed, leading to the most telling mode of attack on many of the pests which assail leaves, flowers and fruit. James Hargreaves once saw a spinning-wheel overturned, when both the wheel and spindle continued to revolve on the floor. As he observed the spindle thus changed from a horizontal to an upright position it occurred to him that if a number of spindles were thus placed, side by side, several threads might be spun at once instead of a single thread. This was the origin of the spinning jenny; an invention which has parallels in the multiple drills, the gang-saws, and other machinery which take a task once executed by a single drill, saw or punch, and simultaneously perform it with ten, twenty, or a hundred drills, saws, or punches. About thirty years before Josiah Wedgwood laid the foundation of his future eminence, a chance observation gave rise to improvement in the earthenwares of Staffordshire. A potter from Burslem, the centre of the potteries and the birthplace of Wedgwood, in traveling to London on horseback was detained on the road by the inflamed eyes of his horse. Seeing the hostler, the horse-doctor of those times, burn a piece of flint, and, having reduced it to a fine powder, apply it as a specific to the diseased eyes, it occurred to the potter that this beautiful white powder, if combined with the clay used in his craft, might improve the strength and color of his ware. An experiment succeeded, and so began English white ware, since manufactured on an immense scale. More important than this discovery of a new use for flint powder was the discovery, also accidental, of electro-magnetism by Professor Oersted of Copenhagen. The incident is thus related in a letter to Michael Faraday from Professor Christian Hansteen:--