$86 History of Mechanical Inventions and 



Mr Walker also made experiments with a light boat 28 feet long, and 

 on a Thames wherry. 



In almost every experiment the resistance showed an increase, amount- 

 ing to the square of the velocity ; but where the velocity was considerable, 

 the resistance followed a still higher ratio, and this in open water. In nar- 

 row canals the increase must be considerably greater. The excess above 

 the square, is ascribed in a great measure to the raising of the water at the 

 bow in high velocities, and to the depression at the stern. 



If with a speed of 24 miles per hour, 30 tons upon a canal be equal to 7^ 

 upon a level rail-road, a speed of five miles per hour, would, upon the prin- 

 ciple of the square, bring the rail-road and canal to an equality ; whereas 

 the above results makes the two modes of conveyance equal considerably 

 under four miles per houry and gives the railway the decided preference at all 

 higher velocities. 



The following tables will show at once the comparative merits of canal 

 and railway conveyance. 



Land Experiments. Water Experiments. 



Velocity per hour, 2 miles 2 miles 



Distance passed over, 2 miles 2 miles 



Power of engine required, I horse 1 horse 



Time occupied, 1 hour 1 hour 



Mechanic power expended, I 1 



Velocity per hour, 4 miles 4 miles 



Distance passed over, 2 miles 2 miles 



Power of engine required, ^2 horse 8 horse by theory, 



more by experiment. 

 Time occupied, i hour \ hour 



Mechanic power expended, 1 hour 4 by theory, more 



by experiment. 

 In these experiments the resistance per superficial foot was only 1,23, 

 whereas in Bossut's experiments it was 1 .854. The cause of this does not 

 well appear ; but we have no doubt of the great accuracy of Mr Walker, 

 and his method is obviously superior to those hitherto used. As he pro- 

 mises to continue the subject, we may expect soon to call the attention of 

 our mechanical readers to new and important results. In the present state 

 of our commerce and manufactures, we consider the main result of Mr 

 Walker's paper, viz. the great superiority of land over water carriage, as a 

 matter of national interest. A fuller account of Mr Walker's experiments 

 will be found in the Phil. Trans, for 1828, p. 15—22. 



3. On the permanent increase of Bulk in Cast-iron by successive heatings. 

 By James Prinsep, Esq. Assay Master of the Mint at Benares. 



In a former paper on .Mechanical Inventions in No. xvii. p. 168, we 

 noticed the highly important experiments of Mr Prinsep on high tempera- 

 tures. In the course of these experiments he discovered the very remark- 

 able fact, that cast-iron acquires a permanent increase of bulk by each suc- 

 cessive heating. This point is determined by measuring the cubic extent 



