Literary Notices. 317 



acid by carbonate of baiwta, not in excess : again evaporated to 

 dryness, mixed with one part sulphur, then with water, and next 

 with six parts nitrate of potash. According to the other method, 

 the glue having been melted in warm water, half the nitrate of 

 potash and then the sulphur are added to it. It is then heated 

 until it assumes a uniform appearance, on which the rest of the 

 nitrate is added. The compound obtained by either of these 

 methods is neither deliquescent nor hydroscopic ; but being made 

 with nitrate instead of chlorate, unless mixed with ordinary gun- 

 powder it burns slowly and without explosion. If mixed with five 

 parts gunpowder it forms a cheap and powerful explosive agent. It 

 is applicable, advantageously, in the formation of fire-works : and 

 when mixed with the appropriate substances, it affords bi'illiantly 

 coloured fires. 



New Application or Photography. — Photography is now being 

 applied to the registration of the pulsations of the heart and arteries, 

 a purpose eminently useful to the physician. The apparatus em- 

 ployed consists of a glass tube, that at one end is widened out into 

 a cone, the base of which is closed with a thin membrane of vulcanized 

 india-rubber. The upper extremity of the tube is inserted in the 

 slit formed in a division placed in a small camera about its middle 

 and at right angles to its length ; the slit being capable of being 

 closed or opened at pleasure, by means of a small moveable screen. 

 The sensitized plate is made to move with a regulated speed by 

 clockwork. When an experiment is to be made, so much mercury 

 is placed in the tube that it will rise to some portion of the slit, 

 within the camera ; and the membrane is laid on the heart or the 

 artery the pulsations of which are to be recorded. Every pulsation 

 disturbs the level of the mercury in the upper part of the tube ; and 

 as light can pass to the sensitive plate only through the tube, a 

 picture having an undulating lower margin is formed. The sensitized 

 plate moves at the rate of one centimetre per second ; but the effect 

 is magnified so that the curve representing it has an extent of fifteen 

 centimetres. The rate and energy of the pulsations of the heart or of 

 any artery is in this way accurately and satisfactorily recorded. 



LITEEAEY NOTICES. 



The Theories of Copernicus and Ptolemy. By a Wrangler. Long- 

 mans. — No proposition, however well established, ought to escape a 

 frequent re-examination, as the development of the human mind is 

 not promoted by the reception of any doctrine, however true, merely 

 upon authority, but rather by a constant search after truth, through 

 the collection of facts, and the operations of reason thereupon. What- 

 ever is taught upon authority only, should be held as a matter for 

 provisional acceptance only, and not advanced higher, until the in- 

 quirer has been able to discover or follow the train of reasoning 



