270 Scientific Intelligence. 



eye, but the relation of number remains the same. Now a leaf of gold 

 as supplied by the mechanician is only ^^-o^xsii-^ ^^ ^^^ ^^^^ ^^ thickness, 

 so that seven and a half of these leaves might be placed in the space 

 occupied by a single undulation of the red ray, and five in the space oc- 

 cui)ied by a violet undulation. Gold of this thictness and in this state 

 18 transparent, transmitting green light, whilst yellow light is reflected; 

 there is every reason to believe also that some is absorbed, as happens 

 with all ordinary bodies. -When gold leaf is laid upon a layer of water 

 on glass, the water may easily be removed, and solutions be substituted 

 for it; in this way a solution of chlorine, or of cyanid of potassium, may 

 be employed to thin the film of gold ; and as the latter dissolves the 

 other metals present in the gold (silver, for instance, which chlorine leaves 

 . as a chlorid), it gives a pure result ; and by washing away the cyanid, 

 and draining and drying the last remains of water, the film is left attached 

 to the glass : it may be experimented with, though in a state of extreme 

 tenuity. Examined either by the electric lamp, or the solar spectrum, or 

 the microscope, this film was apparently continuous in many parts where 

 its thickness could not be a tenth or twentieth part of the original gold 

 leaf. In these parts gold appeared as a very transparent thing, reflecting 

 yellow light and transmitting green and other rays ; it was so thin that it 

 )iobably did not occupy more than a hundredth part of a vibration of 

 ight, and yet there was no peculiar effect produced. The rays of the 

 spectrum were in succession sent through it ; a part of all of them was 

 either stopped or turned back, but that which passed through was un- 

 changed in its character, whether the gold plate was under ordinary cir- 

 cumstances, or in a very intense magnetic field of force. 



When a solution of gold is placed in an atmosphere containing phos- 

 phorus vapor the gold is reduced, forming films that may be washed and 

 placed on glass without destrojnng their state or condition: these vary 

 from extreme thinness to the thickness of gold leaf or more, and have 

 various degrees of reflective and transmissive power ; they are of S^^f^ 

 variety of color, from grey to green, but they^ are like the gold leaves in 

 that they do not change the rays of light, 



When gold wires are deflagrated by the Leyden discharge upon glass 

 plates, extreme division into particles is effected, and deposits are pro- 

 duced, appearing, by transmitted light, of many varieties of color^ amongst 

 which are ruby, violet, purple, green, and grey tints. By heat many of 

 these are changed so as to transmit chiefly ruby tints, retaining always 

 the reflective character of gold. None of thera affect any particular ray 

 selected from the solar spectrum, so as to change its character, otherwise 

 than by reflection and absorption; what is transmitted still remains the 

 same ray. When gold leaf is heated on ghi^ the heat causes its retrac- 

 tion and runnhig together. To common observation the gold leaf disap- 

 pears, and but little light is then reflected or stopped : but if pressure by 

 a polished agate convex suiface be applied to the gold in such places, re- 

 flective power reappears to a greater or smaller degree, and green light is 

 again transmitted. When the gold films by phosphorus have been prop- 

 erly heated, pressure has the same effect with them. 



If a piece of clean phosphorus be placed beneath a weak gold solution, 

 and especially if the phosphorus be a clear thick film, obtained by the 



