Miscellanies. 355 



by the instantaneous reversing of its poles, and so on. The model 

 worked smoothly and with a very uniform, regulated motion, and 

 appeared to be capable of working for a great length of time. Mr. 

 M'Gauley stated, that the erosion of the zinc plate was so inconsid- 

 erable, that there was hardly any limit to the length of time that 

 the model would continue working. The "acid best suited to this 

 purpose, was a mixture of one part nitric, two parts sulphuric, and 

 one hundred water; he also stated, that, in practice, the acid could 

 be always renewed, by having a constant dropping of fresh acid liquor 

 into the trough, while a similar gentle discharge of the spent acid 

 from the trough could be kept up. He stated, that a numerical 

 comparison of the economy of this mode of producing motive power, 

 with that depending upon the agency of steam, would give a vast 

 preponderance in favor of this method, while the part of the power 

 consumed in working the machine itself might be left entirely out 

 of the account, since the apparatus which changed the poles in this 

 model, would equally suffice in a machine capable of working with 

 the power of one hundred horses. In this model, he only worked 

 with one of the two soft iron magnets, and its power was only that 

 of lifting seven pounds, and yet this appeared sufficient to overcome 

 all the friction, inertia, and other impediments to motion, of the sev- 

 eral parts of the machine. 



Heights of mountains, ^c. according to Col. Sykes, are ascer- 

 tained with sufficient accuracy for every practical purpose, by a com- 

 mon thermometer, of accurate construction, applied to boiling water, 

 whose temperature is lower as the station is higher, according to a 

 well known ratio. 



2. Report of the fourth meeting of the British Association for 

 the Advancement of Science. — This handsome 8vo. volume of seven 

 hundred pages, we have just received, as a gift from the Associa- 

 tion. It contains the following important reports. 



1. Report on the geology of North America, Part I, by Prof. 

 H. D. Rogers. 



2. Report on the laws of contagion, by Dr. William Henry, of 

 Manchester. 



3. Report on animal physiology — on the blood and its circulation, 

 by Prof. William Clark, Univ. Cambridge. 



4. Report on zoology, by Rev. Leonard Jenys, M.A. F.L.S. &;c. 



5. Report on capillary attraction, by Rev. James Challis, late 

 Fellow of Trinity College, Cambridge. 



