Hand in hand with the development of the optical apparatus has been the wonderful improvement in regard to the illuminants and the methods of producing a brilliant clear flame. The fuel first used upon the introduction of the oil lamp was sperm or colza oil, the former being obtained from the whale, and the latter from seeds and a wild-cabbage. Both were very expensive, so that the maintenance of a light was costly--so much so that the United States authorities devoted their efforts to the perfection of a high-class lard-oil. This proved highly satisfactory, possessing only one drawback. In winter it congealed so much under the low temperature that it had to be heated before it could be placed in the lamp; but once the light was set going, the heat radiated from the burner served to keep the oil sufficiently fluid to enable it to mount the wick to the point of combustion under capillary action. So far as the American authorities were concerned, the advantages of lard-oil sufficed to bring a cheaper medium than colza-oil into vogue. A company, which had been induced by the Government to install an elaborate and expensive plant for the production of colza-oil, after prolonged experiment and efforts to reduce the cost of production, announced that it could not compete with the lard-oil, and suggested that the latter should be employed in preference to the colza. The Government agreed, but, to compensate the company for its trouble, purchased the plant which the latter had laid down. The advances in the processes for refining petroleum, and the exploitation of the extensive resources of the latter, led to “earth-oil,” in some form or other, being employed for lighthouse purposes. The attempt was facilitated by the invention and improvement of the Argand burner, whereby a brilliant white annular sheet of flame is produced. Various lighthouse engineers devoted their attention to the improvement of this burner in conjunction with paraffin. Their results were completely successful, and at last paraffin became universally utilized as the cheapest and most efficient illuminant known. The general method of feeding the lamps was to pump the oil from a low level to the burner, thereby producing practically a pressure-feed system in preference to the capillary action which is used in the ordinary household lamp. By increasing the number of rings the intensity of the flame was increased, until at last it was thought that with this development perfection had been attained so far as lamps were concerned.