LECTURES. 



175 



paper. These, under the influence of the lime ball light, gave a 

 shadow on the adjoining wall which did not terminate with the 

 outline ol the flame, hut merged without any line of demarcation at 

 the upper part of each flame in a continuous ascending undulatory 

 shadow that reached to the ceiling of the lecture room. The apparent 

 shadow arose from the refraction produced by the heated current of 

 ascending vitiated air, and the necessity was then pointed out of all 

 lamps used in public buildings being ventilated by special tubes, or of 

 ventilating apertures being arranged for tlie discharge of vitiated air 

 above them, so as to prevent the recoil and descent of vitiated air from 

 the ceiling. In an assembly for the transaction of business, m a 

 church, in a school, in courts of law, and in other similar collections, 

 it was too often forgotten that the object to be attained by lighting 

 was not so much to show a beautiful chandelier as to illuminate the 

 countenances of those who took a prominent part in the proceedings. 

 A visible light close to any object, or in the direct line of sight 

 between one person and another, interfered with distinct vision. 

 In a light-house the light was the special object of attention, as in 

 fireworks, and in various optical, electrical, and chemical experi- 

 ments; but in public buildings, such as had been adverted to, the Jess 

 the actual flame or luminous matter was seen the better, provided 

 the proper objects were well illuminated. The more successfully the 

 diffused light of day was imitated, and the light by night corresponded 

 with the light required and given by day, the more satisfactorj^ would 

 the result be. But many were the buildings in which the light by 

 day as well as that by night was very imperfectly adapted to the 

 necessities of the case. In his experience, at least, he had often seen 

 the back of the head illuminated more powerfully than the counte- 

 nance, and a distraction of rays and beams of light utterly at variance 

 with that harmony and unity of effect that was always manifested in 

 an external landscape, when there was no disposition nor attempt to 

 gaze upon the sun itself in its meridian splendor. The different steps 

 in the progress of this question were then explained ; the successive 

 experiments made at Edinburgh, Liverpool, and London, and the final 

 acknowledgment of the principle that the products of combustion from 

 lamps, as well as the heat they produced, should be excluded or with- 

 drawn as much as possible from ventilated buildings, where the heat 

 was not rendered useful in unison with proper ventilation. That 

 electrical lights, oxygenated lights, lime ball, and other lights of 

 great intensity, were not so much required, at their present expensive 

 cost, as a mild and diffused light illuminating the objects to be seen, 

 and which should not glare in the eye of the observer. That the 

 countenance should be illuminated by rays extending from an ex- 

 panded surface, and rather from above downwards, than from below 

 upwards, always securing, directly or indirectly, as much horizontal 

 light as was required. That lights at a low level, as foot-lights, such 

 as are common at theatres, give an unnatural expression to the coun- 

 tenance, and also interfere materially with distinctness of vision when 

 hot currents of air are permitted to ascend from them, by the ine- 

 quality of the refraction of light transmitted through such heated cur- 

 rents and the contiguous colder air. That the new resources placed 



