Letter from John Frederick William Herschel, 2 Orchard Street to [Edward Sabine] Herschel sends information recorded to determine the difference between ‘the indications of his portable barometer by Troughton and a standard thermometer by Newman, and those of various other instruments’, and remarks they may be of interest to the Board of Longitude. Includes a table and description of its contents. The table depicts the instrument compared, difference between the zero point and the portable barometer by Troughton, the difference in the indication of the attached thermometer, as well as remarks. Herschel discusses the ‘results of comparisons of various thermometers with a standard thermometer by Newman’. 4 November 1824