April 1 8, 1878] 



NATURE 



495 



According to this table a hundred parts of the quick-drying 

 white-lead are ground with twelve parts of oil, and on the other 

 hand, the slow -drying ivory -black requires one hundred and 

 twelve parts of oil. 



' It is very important that artists should have an exact 

 knowledge of these matters. But it seems to me that they 

 are insufficiently known to most of them. All, of course, 

 know perfectly how different the drying quality of different 

 colours is. But that these different colours introduce into the 

 picture so different a quantity of oil, and how large this quan- 

 tity is in the colours they buy, and further, that the oil as well 

 as the mediums or siccatives they add to dry the colours, are 

 gradually transformed into a caoutchouc-like opaque substance, 

 which envelops and darkens the pigments ; and moreover, that 

 the oil undergoes — not in the beginning, but much later on when 

 it is already completely dry— changes of volume.and so impairs 

 the continuity of the picture— all this is not sufficiently known. 

 Otherwise, the custom of painting with the ordinary oil colours 

 to be bought at any colourman's, would not have been going on 

 for nearly a hundred years in spite of all the clearly shown evil 

 results ; results due, chiefly, to the principal enemy of oil 



PAINTING, THAT IS TO SAY, THE OIL. 



That the masters of the fifteenth and sixteenth centuries did 

 not use colours prepared in this way you may consider as abso- 

 lutely certain ; and if we hear the lost secret spoken of, and if 

 we read that the pupils of the old masters had to pledge 

 themselves to keep the secret, we may be .sure that it is neither 

 the method of painting nor the pigment u.sed for it which is 

 concerned in that secret, but exclusively the way of preparing 

 the colours. The preparation was a very complicated one, 

 varying with the different pigments ; and we know that the 

 pupils passed six years, that is half of the apprenticeship, in 

 grinding the colours for the master. 



And therefore it is to this very point that everyone who 

 wi-shes to study the method of the old masters must first of all 

 direct his attention. I, too, was led by the study of this ques- 

 tion to analyse and restore old pictures. The possibility of 

 making such analysis we owe to the relation between the old 

 masters and their pupils. Of course we could not dissect or 

 chemically analyse works of Titian or Raphael. But fortu- 

 nately the pupils painted with the same material and by the 

 same method as the masters, and thou.sands of pictures by the 

 pupils, well preserved or in different stages of decay, may be 

 easily procured. 



I have myself, from among a very great number of such 

 pictures, selected about one hundred specimens, part of which I 

 have brought before you. As their artistic value is not, as you 

 perceive, of the highest description, we need not feel any 

 .scruple in experimenting upon or even destroying them, if -we 

 can thereby gain any valuable information. 

 ( To he continued. ) 



GAS-LIGHTING BY ELECTRICITY 



FOR some time past the street lamps in Pall Mall, Waterloo 

 Place, and part of Regent Street, have been connected by 

 wires, which may have led the uninitiated to think that a new 

 method of fixing telegraphic wires was about to be adopted. 

 This is not the case, however, for although the wires were- con- 

 nected with a battery, they were not intended to convey telegra- 

 pjiic message?, but to experiment on a nev^ method of lighting 



.street lamps by means of electricity. The inventor of this 

 method is Mr. St. George I.ane Fox, who recently described 

 his invention to the Society of Arts. vShould Mr. Fox's method 

 be adopted, the wires, instead of running from lamp to lamp 

 above ground, will be carried along under ground, and the only 

 thing visil)le would be a small piece of boxed-in mechanism just 

 under the burner of each lamp. The experiment \\hich was 

 made on Saturday afternoon was not, we believe, completely 

 successful. The magneto-electric machine and the battery which 

 supply the current were ]->l?.ced in a small teniporr.ry instrument- 

 house at the bottom of Waterloo Place. At the first trial the 

 whole of the lamps in the circuit were lighted by the current, 

 though in a second trial some of the lamps failed to respond to 

 the current ; but that this was owing to some local cause is 

 probable from the fact that the first and last lamps in the circuit 

 always responded to the discharge. We shall endeavour to 

 explain the method adopted by Mr. Fox. 



Fig. Z. 



h 



In the first place he supplies every lamp with an apparatus 

 similar to Fig. i j next the lamps must be connected with an 

 insulated conductor, so that, starting from a central station, a 

 wire would travel through each of these machines and back 

 again to the station. Mr. Fox proposes that several of these 

 circuits, each connecting and controlling 200 or 300 lamps, 

 should proceed or radiate from a central station, so that from 

 one point several thousand lamps could be operated upon almost 

 instantaneously. 



The method by which he has succeeded in producing the 

 ignition of the gas at a considerable distance, and at numerous 

 points, is by supplying each lamp with a small induction coil, so 

 that the primary wires of each one of these induction coils 

 forms part of the circuit, so in fact as to preserve without a break 

 the metallic'continuity of the line. After several experiments it 

 occurred to him that in reality the amount of work to be done in 

 producing a number of small electric sparks was extremely 

 minute, although at the same time requiring to be produced 

 almost instantaneously. Now the amount of work which an 

 electric battery will produce is dependent on the time during 

 which action continues, and in a single inttant, or say the thou- 

 sandth part of a second, the actual amount of power available is 

 naturally extremely small, and he thought that if he could by any 

 means accumulate this power for a short time and then bring it 

 suddenly to bear upon the circuit, the desired result would be 

 obtained. By means of an apparatus he succeeded in accumu- 

 lating the electric current and storing it up into the condenser or 



