42 THE ESSEX FIELD CLUB. 



perhaps the oldest forest in existence, belonging to the coal period ; it is at 

 Partick, near Glasgow, and the stumps of the trees are still standing as shown in 

 the picture. He also exhibited slides in relation to "physiography,"' or what the 

 Germans call " Earth knowledge."' Some of them illustrated the ways in which 

 rivers cut valleys through both soft earth and hard rocks. 



Prof. Meldola then came to the use of photography in physics. He explained 

 the analysis and synthesis of white light, and spoke of the photographing of the 

 spectrum. He exhibited a solar spectrum with plenty of lines in it, which he had 

 taken when associated with Mr. Norman Lockyer some years ago. He also told 

 of Dr. H. W. Vogel's origination of orthochromatic photography in 1874, and 

 how that branch of photography has been extended by the researches of Mr. C. 

 H. Bothamley, technical organiser for the county of Somerset. He dealt with 

 the wave theory of light, the phenomena of interference, and stated that the first 

 scientific use of photography was made in 1803 by Dr. Thomas Young, in photo- 

 graphing Newton's rings at the Royal Institution. Lord Rayleigh has just been 

 photographing interference bands, applying the phenomena to the revealing of 

 the degree of approximation to truth of asserted truly plane glass surfaces. Some 

 of the results, lent to the lecturer by Lord Rayleigh, were exhibited on the screen. 

 The photographs had been taken by pure sodium light, and plates made ortho- 

 chromatic by ammoniacal cyanin. 



The lecturer lastly spoke of the " inductoscript " taken upon photographic 

 plates without light, by the Rev. Professor Smith, of Oxford. Electricity of 

 rapidly alternating current was used ; a coin was connected with one terminal, 

 and a sensitised plate with the other, and the coin and plate were brought very 

 near to one another. Then all light being excluded, the current was switched on 

 and was continued for fifteen minutes. At the end of that time the plate was 

 developed, and there was an image of the coin. A striking feature of it was that 

 from every projection in the milling there was a brush of rays, as one sometimes 

 sees depicted round the sun in old paintings. Prints could also be copied b}' this 

 process. Prof. Meldola said that he could not explain the production of this 

 picture ; the thing was not understood, it had yet to be investigated. 



The Chairman, Mr. T. V. Holmes, in moving a vote of thanks to the lecturer, 

 remarked that Prof. Meldola was well aware of the extent to which photography 

 was being utilised by the British Association, because he was the Chairman of the 

 Committee of the Corresponding Societies connected with the Association, ol 

 which societies the Essex Field Club was one of the chief. He hoped that its 

 members would help to supply the photographs the Association required The 

 value of photography in geology was very considerable, and in two instances 

 which had occurred lately within his own knowledge in Essex, he had regretted 

 the absence of such a truthful record of observation. In surveying the railway 

 cutting between Upminster and Romford for his paper in the EsSEX Naturalist 

 (vol. vii., p. i), he had found Boulder-Clay three miles farther south than had 

 previously been known. He had taken several geologists to the spot in order 

 that they might see the evidence of the fact with their own eyes, but a good 

 photograph would have been a sufficient record without further trouble. Again, 

 in the Romford cutting of the same railway, he had seen evidence of the existence 

 of an old river-bed, but a day or two later, when revisiting the spot with some 

 geological friends, the ground had been sloped, and in the absence of photographs 

 all chance of showing his friends what he had seen on former visits had vanished. 

 The river at Wakefield had been favoured in the photograph shown by Prof. 



