410 British Association for the Advancement of Science. 



scale of the operation, and substituting metal for glass. A highly 

 polished metallic vessel, not more than -Jths of an inch wide and 

 H inch long, is nearly filled with water ; some crushed sal ammo- 

 niac is introduced ; the salt is stirred up and mixed with the water 

 by the bulb of a small thermometer, which falls in consequence 

 very gradually, and when the dew appears the thermometer is in 

 contact with the surface on which it is deposited. If a consider- 

 able depression of temperature is required, the vessel may be 

 cooled down previous to the experiment by a similar process. This 

 instrument, from the small quantity and cheapness of the cooling 

 material, may be used constantly without extravagance, and from the 

 conducting and radiating properties of the vessel, as well as the pre- 

 cision with which it indicates the first deposition of dew, may pro- 

 bably be found to be uniform in its results. 



Mr. Moore laid before the Section a leaden pipe which had 

 served for about twenty years as the worm of a still, for the distil- 

 lation of medicated waters and spirits ; at length it began to leak, 

 and on examination it wan found to be supported at various points 

 by bars of wood crossing it, and to be tied at others with twine. 

 Wherever it thus came in contact with either wood or twine, it was 

 deeply corroded, and the lead appeared to be converted into a dark 

 powder, which, when examined, was found to contain oxide and 

 chloride of lead ; at all other points the pipe was perfectly sound, 

 The appearance of the corroded parts was sufficiently against its 

 being attributed to mechanical action. The presence of chloride 

 and oxide in the powder, established, he thought, that the corrosion 

 was not entirely, if at all, caused by acids formed by the decaying 

 organic matter ; it appeared to him that it ought rather to be attri- 

 buted to galvanic action, developed by the contact of the metal, and 

 wood, or twine, which cause, acting for such a length of time, might 

 be sufficient to accomplish the destruction of the pipe at the points 

 of contact. 



Notice of certain Appearances in Coagulated Blood. By 

 Dr. Newbigging. 



The author has observed on the under surface of a clot of blood, 

 received into a cup variously coloured within, certain bright red 

 spots, corresponding accurately to the figure of those parts of the 

 interior of the cup which were coloured green, while in all other 

 parts the coagulum was of a dark tint. Experiments were tried on 

 various sorts of china, with different colours and glazing, but always 

 with the same result. The contrast of the brightness of these red 

 spots with the darkness of the general mass lasted nearly ten minutes 

 after exposure to the air. 



On a Modification of the Safety Lamp. By W. Ettrick. 

 The author, referring most of the unfortunate explosions which 



