118 



THE CIVIL ENGINEER AND ARCHITIXT'S JOURNAL. 



[April, 



only in beinj; submerged and placed behind tlie rudder. In 1838, it being 

 ascertiilued that a perfect screw of one or two turns could not be worked 

 by the obstruction of the back water, Mr. Lowe took out a patent for cut- 

 ting the screw into arms or blades, which worked between the rudder and 

 the stern-post. In April, 183y, .Mr. Smith entered a memorandum of dis- 

 claimer, by which he slated that he found that a screw of two turns would 

 not do, that the true principle was to take two half turns of a screw planted 

 in the centre of the 'dead wood." After explaining the evidence that he 

 had to produce as to the usefulness of Mr. \V oodcroft's invention, jMr. Jer- 

 vis concluded — Having expended 1,201)^ and upwards in pushing his in- 

 vention, and having only received in return about 130(., Mr. M'oodcroft 

 was entitled to such a renewal of his patent as would enable him to re- 

 munerate himself, not only for capital laid out, but for the trme and talent 

 which he had spent upon it. Mr. W'oodcroft had made several other in- 

 veulious, and in appljing for a renewal of his patent, he proposed intro- 

 ducing an improvement on the original plan, by which to alter at pleasure 

 the variations in the " pitches." 



Mr. Carpniael stated that he had studied the subject of the screw pro- 

 peller for several years. In the use of ordinary screws, tiie water was put 

 in motion by the first part of the screw, and being of ihe speed of the second 

 part of the screw, choked the screw. The advantage of this screw was 

 that the second part was so constructed as to outstrip the motion of Ihe 

 water, so that the instrument was an operative one, whatever might be its 

 length. All other screws consisted of a straight line wound round a cylin- 

 der, but that of Mr. Woodcroftwas a circle, or segment ot it, wound round 

 a cylinder. Tredgold, in his work on propulsion, proposed that the screw 

 should go on with a decreasing angle on an increasing pitch, but he stated 

 nothing about a circle wound round a cylinder, which was Jlr. Woodcroft's 

 principle. 



Cross-examined by the Solicitor General. — Mr. Corameraux's patent 

 was a spiral by language, but a screw by description. The word " spiral" 

 or " screw" did not truly designate the distinction. The word " helix" 

 was used at present. He had seen the screw of Mr. Woodcroft in a vessel 

 at Bristol, which had come in from sea about three years ago. With that 

 exception he had never seen it in use. He had never known a screw used 

 practically till the time of the Archimedes, in 1839 and 1840. From that 

 time the use of the screw had increased greatly, both in the Royal and 

 mercantile navy. The screw he saw at Bristol was only one fourth of a 

 convolution, and a three-threaded screw. lu practice it was called the 

 one-eighth of a convolution. He had never seen the ordinary screw in 

 operation of more than one convolution ; but as far as his experience went 

 it would not work. He was satisfied that Mr. Woodcroft's spiral would 

 work with more than one convolution. The varying angle would, he 

 thought, operate all through. The spiral was between the stern-post and 

 the rudder-post, raised for the purpose. Smith's patent was placed in the 

 dead wood. Woodcroft's was not technically a spiral, because it did not 

 run up to a point. 



Mr. S. Slaughter said he bad built two vessels fitted up with Mr. Wood- 

 croft's ''spiral." He had tried other screws in the vessel before Mr. 

 Woodcroft's, and he greatly preferred the latter. 



Cross examined by the Solicitor-General. — The other screws he had tried 

 were not under any patent, and had varied from one-fourth to oue-tenlh of 

 a convolution. He tried nine screws of varying diameter and the same 

 pitch. Being dissatisfied he tried an increasing pitch and found the ad- 

 vantage of it. He had thus accidentally stumbled on Mr. Woodcroft's in- 

 vention, and finding thai, he applied for a license. Wilh Mr. Woodcroft's 

 he had attained a speed of i4 miles an hour, while with others he had only 

 secured a speed of seven or eight miles an hour. In the one case the water 

 " slipped" olTthe blades, and in the other it did not. 



Mr. Murray, assistant-engineer to the Admiralty, said that he could 

 speak to two trials, one on Ihe 13lh of April last, and the other on the 18th 

 of March, in which Ihe relative merits of Mr. Smith's and Mr. Woodcroft's 

 invention had been attested. With that of the former the results were as 

 follows : — With the engine giving 26-28 strokes the rate of speed was 8- 18 

 knots, the slip being 3 143. or 27-758 per cent., and the revolution per 

 minute 104.34. Mith that of Ihe latter the results were— wilh the engine 

 giving 24-152 strokes a revolutio.-i per minute of 95-99. a speed of 8-159 

 knots and a slip of 2-155, or 23502 per cent. The result exhibited in Mr. 

 Woodcroft's favour a speed nearly as great, with less power of the engine, 

 and much less slip. If the facts which he had staled were reduced, a dif- 

 ference would be shown of one-sixth of a knot per hour in favour of Mr. 

 Woodcroft. He was aware that by other experiments Mr. Smith's screw 

 had attained a greater velocity. 



Mr. Cowper, an engineer, said, that the invention was a new and very 

 ingenious one. He illustrated its effect by an experiment on the air with 

 tin blades modelled after Mr. Woodcroft's screw, and which when spun 

 rapidly round on an axis by a piece of twine, as a lop is spun by a boy, 

 flew up wilh great force to the eeiliug. When the side was reversed, and 

 the experiment repeated, the model was not moved from the axis it re- 

 volved on. 



The Solicitor-General submitted that the present was no case of a useful 

 invention at all. There was nothing new in the idea of using a screw for 

 propelling vessels, as it had been in existence as long ago as 1794. It wa» 

 Mr. Smith's discovery that the screw should be placed in the centre of the 

 dead wood which first led to its practical utility. When Ihe screw was so 

 placed and reduced to between one-fouith and one-eighth of a convolution 

 all other points with regard to its construction became immaterial. Before 



Mr. Smith's invention the screw was placed in unsuitable parts of Ihe 

 vessel, and none of them had ever succeeded. The Solicitor-General then 

 proceeded to explain, wilh reference to the models produced in court, that 

 it was only by adopting Mr. Smith's discovery and inserting the screw in 

 the dead w-ood that .Mr. M'oodcroft had succeeded in making a practical 

 application of his patent. He read an extract from the specification of the 

 latter gentleman, the strongest point in which was as follows : — "The 

 spiral propeller may also be placed under the stern of the vessel, as seen 

 in figures 5 and C, where a part of Ihe hull is removed." The improve- 

 ment claimed by him had nothing to do with Ihe position, but was one in 

 reference to an increasing angle. At the time when Mr. Woodcroft took 

 out his patent it was no improvement at all, for want of the discovery that 

 it should be placed in the dead wood. 



Lord Brougham. — But it is now beyond a doubt that some steamers 

 may have no " dead wood" at all. 



The Solicitor-tieneral. — I'ractically it might be so in the case of a Dutch 

 built vessel, but not one for steam communication. In all vessels there 

 was but one slerupost, and it was playing wilh language to introduce the 

 terms which had been used in the evidence, lie should refer to Mr. Wood- 

 croft's specification hereafter, but in the mean time he would ask if the 

 space filled by Mr. Woodcroft's screw were not so occupied, would it not 

 be the "dead wood." If so, then Mr. Woodcroft's screw was inserted in 

 the dead «ood. In his drawing there was no continuation of the keel, but 

 an undue prolongation of the deck, and a stern-post to which Ihe rudder 

 was attached. No particular ratio of angular increase or decrease was 

 claimed by Mr. Woodcrofi, and Mr. Conmieraux had already discovered 

 the principle. In the patent of the latter the term •' spiral" was used, and 

 in the drawing the increasing angle was clearly marked. The convolutions 

 in the drawing were as three to two. 



Mr. Cowper was here recalled, and stated that there was no intimalioo 

 of an increased pitch in the drawing, even taking into account the word 

 spiial in the specification. 



The Solicitor-General then gave up that point, and proceeded to argue 

 that as Mr. Woodcroft had in his specification only provided for one con- 

 volution or more, and as there was only evidence of its answeritig for one- 

 eighlh of a convolution, there was no direction in the specification which 

 would guide a workman to the only form of the invention which bad prac- 

 tically been found to answer. 



Lord Brougham. — The drawing No. 12 shows only one-eighth of a con- 

 volution, being esaclly what is now used. His claim is quite general. 



The Solicitor-General. — Mr. Carpmael had stated that Ihe spiral would 

 work wilh any number of convolutions, but notwithstanding the amount of 

 experience on the subject now, not more than one-quarter of a revolutioQ 

 had in any screw been found to answer. Afler 14 years' opportunity for 

 experiment, it had been so, and the onus probajidi therefore lay on Mr, 

 Woodcroft, for showing that the spiral would work at more than one revo- 

 lution. 



Lord Brougham delivered the judgment. In all cases where there was 

 a disputed right as to patent, and where Ihe validity of the patent might 

 come into question, there were two things to be considered. 'The first was 

 whether Ihe case to prove the invalidity of Ihe patent was so clear as to 

 remove all prdiiiary doubt ; the second was whether the case was so doubt- 

 ful that that Court would rather retire from its consideration and not de- 

 cide it. In the former case they would nol grant the extension, because 

 they did not see the merits, and because they would not put Ihe opposing 

 parlies to the vexatious process of bringing their scire facias in the law 

 courts. But %vhere Ihe matter was doubtful — where confiicling evidence 

 and questions of law equally arose, that Court would not refuse the discre- 

 tionary power vested in them by Parliament merely because it was also a 

 case in which the valid:ty of the patent was contested. The present case 

 came under the first principle he had slated. There was nothing to make 

 it clear that the patent should not be sustained until they took away the 

 merit of the invention. If the patent turned out to be invalid, it would 

 only be the extension of such a patent for so many years. Now, as to the 

 merits in this case there could be no doubt. His Lordship gave it as his 

 own opinion on a scientific point, that Mr. Woodcroft's invention was a most 

 ingenious application of mathematical principles to mechanical ends, and 

 he commented on the evidence which had been adduced on Ihe subject. 

 It was not enough to object that Ihe patent had been long in coming into 

 operation, for the steam-engine, and many other discoveries, were open to 

 the same observation. All his time, his ingenuity, and his labour had pro- 

 bably been exhausted by Mr. Woodciott on this work. They had every 

 reason to believe that he would be for the next few years in happier cir- 

 cumstances, and more likely to receive compensation. On the grounds he 

 had staled, their Lordships were of opinion that a period of six years should 

 be given by way of extension to the petitioner. What he had said was 

 without reference to Mr. Smith's invention, which might be a most ingenious 

 one. 



The Skew Arch an Old Invention. — "Now visiting the Alcazar 

 (cathedral at Sevdle), but first observed a singular Moorish skew arch, in 

 a narrow street leading from the cathedral to the Piierla de Xeres ; it 

 proves that the Moors practised Ibis now assumed modern invention at 

 least eight centuries ago." — Ford's Spain. 



