1882.] Temperatures of the Water of the Thames, 8fc. 



277 



the trunk so as to be about 2 feet below the surface of the water and 

 1 foot above the bottom of the trunk. 



"In 1870, April, the observations at the 'Dreadnought' termi- 

 nated ; in 1871, January, observations were recommenced at the police- 

 ship ' Scorpion,' moored in Blackwall Reach (between Greenwich 

 and Blackwall), the thermometers being mounted in the same way as 

 previously at the 'Dreadnought'; in 1874, May, the wooden trunk 

 and thermometers were removed from the ' Scorpion ' to the police- 

 ship 'Royalist,' moored in the same place. In 1879, October, the 

 1 Royalist ' was damaged by another vessel coming into collision with 

 her ; after repair, the ' Royalist ' was not again moored in the river, 

 but was placed on the river bank near high- water mark, in which 

 position no further observations of the temperature of the water could 

 be made. The observations have not, to the present time, been 

 resumed in any other position. 



"The instruments employed throughout were one for highest tem- 

 perature and one for lowest temperature. For highest temperature 

 two constructions have been successively used ; the earlier, in which 

 the mercury, with rising temperature, pushes up a steel index, leaving 

 it detached when the temperature falls ; the later, in which the 

 column of mercury becomes divided on fall of temperature, the 

 principal portion of the column being left in the tube. For lowest 

 temperature a spirit thermometer was employed, its index being con- 

 tained within the column of spirit. The index-errors of the two 

 thermometers in use were properly determined, and corrections for 

 them were applied when necessary. 



"The thermometers were read every morning at 9 a.m." 

 In the first steps of publication of these observations in the 

 Greenwich Meteorological Table, given in the Registrar- General's 

 " Weekly Report of Births and Deaths in London," the printed 

 readings, in early years, were referred to the civil day preceding that 

 on which the instruments were actually read ; in later years they 

 were referred to the civil day on which the instruments were read. 



The observations of atmospheric temperature at the Royal Obser- 

 vatory were made with the maximum and minimum thermometers 

 in ordinary use, at the elevation 4 feet above the ground ; readings 

 adopted here are those which correspond to the civil day preceding 

 that on which the Thames thermometers were read. 



It will be remarked that the indications of the thermometers in the 

 Thames were read only once in each day. I could have wished that 

 a greater number of readings could have been taken, sufficiently 

 numerous to exhibit the dependence of the temperature of the Thames 

 water upon the phase of the tide. But under the circumstances this 

 was impracticable. To establish a self-registering apparatus was out 

 of the question ; and if on a few occasions we had gone through the 



