TRANSACTIONS OF THE SECTIONS. 263 



obviates the jarring, dislocating and shaking which ensue when the wheels are sud- 

 denlylocked at a high rate of speed. Its application by steam power and complete 

 control by the engineer also ensure its instant application when needed ; and the 

 wheels will last longer from being spared the friction of the breaks and rails. But 

 the result of these advantages combmed being to enable a train to be brought to a 

 stop in a much shorter distance than is now eifected, was the most striking benefit 

 anticipated fi'om its introduction. 



On Pliotozincography, hy means of luJiicJi Photographic Copies of the Ordnance 

 Maps are chiefly multiplied, either on their original or on a reduced or 

 enlarged scale. By Colonel Sir Henkt James, B.E., F.B.S. 



The process is applicable to the reproduction of old manuscripts and old printed 

 books, and any line engTaviag. A copy of Domesday Book (the part relating to 

 Cornwall taken by this means) was exhibited to the Meeting. The process consists 

 in taking a photographic coUodion negative, which is intensified by means of bi- 

 chloride of merciuy and hydi-oaulphiu-et of ammonia. Paper, deprived of its size, 

 is satiu-ated with a solution of gelatine and bichromate of potash. The paper thus 

 prepared is exposed to the light beneath the negative, the result of which is that 

 the parts which have been exposed to the light become insoluble.^ The whole is 

 then inked with a gi-easy ink and afterwards washed in water, which removes the 

 ink from all the parts except those on which the light has acted. A transfer to 

 stone or zinc is then taken in the ordinary way, and copies are printed. The author 

 then described an improvement which had lately been made in the process, by 

 means of which a reduced copy of a map or plan could be made, in which the 

 minor details (which would be useless on a reduced scale) coiild be omitted, and the 

 names of places and other features of the plan given in full-sized legible characters. 



On the Application of the Direct- Action Principle. By W. B. JoHNSOjr. 



The author said that whilst immense improvements had been made in almost 

 every other class of machineiy, the stationary beam-engine remained ahnost in the 

 same state as when it left the hands of the earliest makers, and may consequently 

 be regarded as one of the most imperfect pieces of mechanism of the present day. 

 Comparing the beam with the direct-action engine, he said the latter are superior 

 in the following points : viz., they are independent of the foundation and engine- 

 room walls for sti-ength and support ; they are less liable to derangement and 

 breakage, and such cases are attended vdth less serious results ; offering also great 

 advantages ia the accessibility to the condensing apparatus and all other working 

 parts of the engine. 



On Patents considered Internationally. By R. A. Macfib. 



On the Besistance of Ships. By Professor W. J. MACQTroKN Rankine, F.B.S. 

 The author states that the investigation to which this paper relates w^as founded 

 originally on experimental data supplied to him by Mr. James E. Napier in 1857, 

 and that its results were successfully applied to practice in 1858 and subsequently, 

 to calculate beforehand the engine-power required to drive at given speeds ships 

 built by Mr. J. R. Napier. He refers to pre\ious investigations of the effect of 

 friction in resisting the motion of a ship through the water ; but remarks that 

 those investigations could not be expected to yield definite results, because in them 

 the velocity of sliding of the particles of water over the ship's bottom was treated 

 as sensibly equal to the speed of the ship ; whereas that velocity must vary at 

 different points of the ship's bottom, in a manner depending on the positions of 

 those points and the figure of the ship, being on an average greater than the speed 

 of the ship in a proportion increasing with the fulness of the ship's lines. _ He then 

 explains the general natiu-e of the mathematical processes by which the friction can 



