34 



ON M. MARIE DAVY'S NEW ELECTRO-MAGNETIC ENGINE.— PHOTOGRAPHY. 



[1854. 



surfaces ; but this arrangement produces, during the action of 

 the machine, a series of shocks or concussions, which are op- 

 posed to the coustruetion of a powerful machine upon this model. 



M. Marie makes the moveable electro-magnets or armatures 

 revolve in such a manner as to approach the fixed electro-mag- 

 nets in the direction of the axis up to the point of contact, 

 without any shock. Upon this principle are constructed the 

 two electro-motive machines described in his note, one of which 

 has a continuous rotatoiy, the other an oscillatory motion. We 

 shall only refer to the former apparatus, of which he has pre- 

 pared a model, which has worked in our presence. 



This machine consists of 63 electro-magnets, arranged at 

 equal distances round a circle of wood, furnished internally 

 with a circle of copper. All the electro-magnets have their 

 axis directed towards the centre of the wheel, and their surface 

 coincides with the concave surface of the copp:r circle. 



In the interior of this large wheel there are two others, of 

 which the radius is one-third of that of the former ; these are 

 also furnished with a circle of copper, and bear each 21 equi- 

 distant electro-magnets, of which the axis are directed towards 

 the centre, and the polar surfaces coincid_e with the concave 

 surface of the copper wheels; these little wheels can then re- 

 volve, without slipping, in the interior of the large wheel, and 

 carry round by their movement the axle of the machine, which 

 corresponds with the axis of the large wheel. The moveable 

 electro-magnets come successively in contact with the fixed 

 electro-magnets. The large and small wheels are furnished 

 with teeth for the maintenance of the coincidence, when this 

 is once established. 



The machine is also provided with various pieces of appa- 

 ratus for putting each of the electro-magnets successively in 

 communication with the battery, and giving a different mag- 

 netization to the two electro-magnets at the moment when they 

 act upon each other. * 



M. Marie has made a change which appears advantageous, 

 by replacing the internal wheels by others, which, instead of 

 bearing electro-magnets, are surrounded by a ring of soft iron, 

 which forms the armature; the moveable portion is thus ren- 

 dered lighter, and the teeth are rendered unnecessary. It is 

 this modification of the machine that we have seen in action. 

 The circular electro-magnets of Mr. Nickels will here find an 

 interesting application ; and, at our suggestion, M. Marie pro- 

 poses to make some experiments with this addition, which will 

 enable him to augment the power of the machine without in- 

 creasing the expense. 



The construction of the machine is somewhat affected by the 

 inexperience of the maker, so that it required a battery of 24 

 Bunsen's elements to produce l-23d horse power. But, ac- 

 cording to M. Marie's calculations, one of the same energy, or 

 perhaps even one of less intensity, would be sufficient, with a 

 machine of large size, to produce 300 times the power, seeing 

 that the friction would not increase in the same proportion as 

 the force of the machine; the means of electrical communica- 

 tion not being changed, and the power produced by the attrac- 

 tion of the magnets being capable of multiplication iu a great 

 degree, by making use of electro-magnets formed of large 

 cylinders of soft iron. The model was constracted with a view 

 to show the relations between the effect calculated from the 

 magnetic force developed in the electro-magnet, and the actual 

 force produced. The proportion was as 4 to 3, which is already 



a veiy close approximation, considering the numerous imper- 

 fections resulting from the bad construction of the machine. — 

 Comptes Rendus. 



Photography. 



WAX PAPER PROCES.S. 



At the last meeting of the Photographic Society, a paper was 

 read by Mr. Townsend, giving the results of a series of experi- 

 ments instituted by him in reference to the wax-paper process. 

 One of the great objections hitherto made to this process has 

 been its slowness, as compared with the original Calotype 

 process, and its various modifications ; and another that its prepa- 

 ration involved some complexity of manipulation. Mr. Towns- 

 end has simplified the process materially, having found that the 

 use of the fluoride and cyanide of potassium, as directed by Le 

 Gray, in no way adds to the efficiency of the process, either ia 

 accelerating or otherwise. The iodide and bromide of potassium 

 with free iodine give a paper which produces rapid, sure and 

 clean results. He discards whey, sugar of milk, grape sugar, 

 &c., hitherto deemed essential, but which his experience shows 

 to be unnecessary. He exhibited three negatives of the same 

 view taken consecutively at eight o'clock in the morning, with 

 the respective exposures of 30 seconds, 2 J minutes, and ten 

 minutes, each of which was good and perfect. The formula he 

 adopts is : — 



Iodide of Potassium 600 grs. 



Bromide of Potassium, from 150 to 250 „ 



Re-sublimed Iodine 6 „ 



Distilled Water 40 oz. 



The waxed papers are wholly immersed in this solution, and 

 left to soak at least two hours, and are then hung to dry in the 

 usual way. The papers are made sensitive by wholly immersing 

 them in aceto-nitrate of sOver of the following proportions : — 



Nitrate of Silver .... 30 grs. 



Acetic Acid 30 minims. 



Distilled Water .... 1 oz. 



the papers remaining in this solution not less than eight 

 minutes. They are washed in two waters for eight minutes 

 each, and then blotted off in the ordinary manner. Mr. Towns- 

 end states that there is no need to fear leaving the paper in the 

 sensitive bath too long. He has left it in the bath 14 hours 

 without any injury. The paper thus prepared will keep ten or 

 twelve days; it may be longer, but his experience does not ex- 

 tend beyond that time. With paper thus prepared a portrait 

 was exhibited, taken in 55 seconds, in a room with a side light, 

 but it. must be added that in this instance the paper was not 

 washed, but was blotted off immediately on its leaving the 

 sen.sitive bath, though not iiscd until two hours had elapsed. — 

 Mr. Townsend used for developing a saturated solution of gallic 

 acid with a dram of aceto-nitrate to every four ounces of it, but 

 he considers that this proportion of aceto-nitrate may be bene- 

 ficially lessened. Ho finds that by this process he is certain of 

 success, and is never troubled with that browning over of the 

 paper which so often attends the use of the other methods of 

 preparation. Besides the rapidity of action which he states, 

 there is the further advantage that a lengthened exposure is not 

 injurious. The proportion of bromide may vary from 150 grs. 

 to 250; less than 150 is not sufficient to produce a maximum 

 of rapidity, whilst more than 250 adds nothing to the effect. 



