TRANSACTIONS OP THE SECTIONS. 



169 



water in the box next morning was found to be 87° Fahrenheit, being a loss of 16°, 

 or little more than one degree per hour. 



The conclusions to be derived from the foregoing experiments are as yet uncer- 

 tain. That the evolution of heat by fluid friction has been proved, cannot be doubt- 

 ful, as has been shown by the refined experiment of Joule ; but by what law re- 

 mains to be determined by future experiments. 



Experiments to determine the Resistance of a Screw when revolving in Water 

 at different Depths and Velocities. By George Rennie, F.R.S. SfC. 



The experiments which have hitherto been made upon screw propellers, have had 

 for their object, principally, to determine their forms and proportions, to enable 

 them to act most effectively in propelling the vessels to which they were attached, 

 and at the same time to impede by their form as little as possible the vessel's mo- 

 tion through the water when under steam or sail. 



In every case it has been considered necessary to give as large a diameter to the 

 screw as the draft of the vessel would admit, in order that the area of its whole disc 

 should have as large a proportion to the midship section and resistance to the on- 

 ward motion of the vessel as possible. So that the present state of our knowledge 

 upon screw propulsion is confined to the best form and ai'ea of the propeller and of 

 the vessel to which it is attached. 



The experiments of Mr. Barlow on several of Her Majesty's paddle wheel vessels, 

 and of Mr. Lloyd on the propelling powers of Her Majesty's steam sloop ' Rattler,' 

 and the recent investigations of Mr. Charles Atherton, had already established cer- 

 tain relations between these extremes. But no experiments have as yet been re- 

 corded on the action of screw propellers immersed at different depths and driven at 

 high velocities. 



Last year my attention was called by Mr. Joseph Apsey, an engineer of Broad- 

 wall, in the parish of Christ Church, Surrey, to some remarkable properties which 

 he stated to have discovered in a double screw which he had invented, but which 

 was similar in every respect to the screw used in the Archimedes steamer. 



The screw which he experimented upon was of brass 13f diameter, 28 inches 

 pitch, and 145 square inches, or about 1 foot area. The screw was fixed upon an 

 iron spindle resting in bearings, one being a stuffing-box on the outside of a boiler 

 in which the experiments were made, so as to prevent leakage, and the other end 



Mr. Apsey's Experiments. 



loose in the bearing fixed at the bottom of the boiler. A pulley of iron was fixed 

 to the outer extremity of the spindle, so as to allow of its being driven by leather 

 bands at any rate of speed. A bracket was bolted to the outside of the boiler for 

 the purpose of serving as a fulcrum to a bent lever, the horizontal extremity of 

 which supported a scale and weight, and the vertical extremity was pushed by the 

 screw when revolved in the water in the boiler, so that the weights lifted by the 

 bent lever indicated the thrust of the screw. 



