238 Messrs. Negretti and Zambra [Mar. 12, 



They are closely similar structures; but there does not appear to be 

 any reason for considering them " serial homologues," or more closely 

 related than are, say, the hairs on the head of a man with the hairs on 

 his chest. 



II. " On a New Deep-sea Thermometer." By HENRY NEGRETTI 

 and JOSEPH WARREN ZAMBRA. Communicated by Dr. CAR- 

 PENTER, F.R.S. Received March 5, 1874. 



The Fellows of the Royal Society are perfectly aware of the assistance 

 afforded by Her Majesty's Government (at the request of the E-oyal 

 Society) for the purpose of deep-sea investigations, and have been made 

 acquainted with their results by the .Reports of those investigations 

 published in the ' Proceedings of the Royal Society ' and by the in- 

 teresting work of Professor "Wyville Thomson. Among other subjects, 

 that of the temperature of the sea at various depths, and on the bottom 

 itself, is of the greatest importance. The Fellows are also aware that 

 for this purpose a peculiar thermometer was and is used, having its 

 bulb protected by an outer bulb or casing, in order that its indications 

 may not be vitiated by the pressure of the water at various depths, that 

 pressure being about 1 ton per square inch to every 800 fathoms. This 

 thermometer, as regards the protection of the bulb and its non-liability 

 to be affected by pressure, is all that can be desired ; but unfortunately 

 the only thermometer available for the purpose of registering tempera- 

 ture and bringing those indications to the surface is that which is 

 commonly known as the Six's thermometer an instrument acting by 

 means of alcohol and mercury, and having movable indices with delicate 

 springs of human hair tied to them. This form of instrument 

 registers both maximum and minimum temperatures, and as an ordinary 

 out-door thermometer it is very useful ; but it is unsatisfactory for 

 scientific purposes, and for the object which it is now used (viz. the 

 determination of deep-sea temperatures) it leaves much to be desired. 

 Thus the alcohol and mercury are liable to get mixed in travelling, or 

 even by merely holding the instrument in a horizontal position; the 

 indices also are liable either to slip if too free, or to stick if too tight. 

 A sudden jerk or concussion will also cause the instrument to give 

 erroneous readings by lowering the indices, if the blow be downwards, 

 or by raising them, if the blow be upwards. Besides these drawbacks, 

 the Six's thermometer causes the observer additional anxiety on the score 

 of inaccuracy; for, although we get a minimum temperature, we are 

 by no means sure of the point where this minimum lies. Thus Professor 

 Wyville Thomson says (' Depths of the Sea,' p. 139): " The determina- 

 tion of temperature has hitherto rested chiefly upon the registration of 

 minimum thermometers. It is obvious that the temperature registered 



