1880.] On Actinoinetrical Observations, made in India. 159 



8. Accordingly, during the present series, this time- range was made 

 one of the objects of inquiry ; it would most probably be found to 

 occupy an equal hour angle, + and — from the meridian, a point, 

 however, which was itself included in the investigation, by providing 

 that the observations should be made continuous for each day. 

 Eventually, the hour angles adopted were 30 m E., and 30 m W., 

 whereby 21 observations in and 20 in X would be obtained, yield- 

 ing ten results before, and as many after apparent noon, by the tabula- 

 tion of Article 6 ; always provided that the observer missed none of 

 the numerous readings, a result which requires some practice to secure 

 in a series exacting continuous attention for so long a period as one hour. 

 In addition to these daily time-range series, the observers were also to 

 take a long range or hourly series (i.e., at every hour, from 8 a.m. to 

 4 p.m.), on two days, each comprising six observations in and five 

 in shade, so arranged that the middle result should occur at the hour. 

 The whole of the simultaneous results thus obtained at Dehra and 

 Mussooree are tabulated according to Article 6 in Table V, and may 

 be briefly explained, thus : — 



9. Table V. — The times are the means of the times of x observa- 

 tions : they are given by preference in entire minutes, to avoid the 

 needless statement of seconds ; but the exact second, or local apparent 

 time, if required, can be readily found by applying to the chronometer 

 time the error in seconds given for each day ; thus, on October 31st, 

 the chronometer was fast on apparent time by 5 s ; this error will 

 always be found to be under + 30 s . The angle between the two local 

 meridians is 4 S, 2, Mussooree being east of Dehra. The results in sun, 

 or (heafc gained), and those in shade, or x (heat lost), are the 

 observed results reduced to 32° Fahrenheit;* from these, for both 

 A and B, there follows directly the radiation or + X glass on, which, 

 in the case of A, was converted, by means of factor No. 1, Article 2, 

 into glass off; in the case of B, the factors Nos. 3 and 1, were suc- 

 cessively employed to express in terms of A respectively glass on and 

 glass off. Thus the whole procedure in reduction was exactly the 

 same as that followed in 1869. Further, the means of the results 

 before and after noon are given separately together with the estimate of 

 accuracy indicated by their "mean errors;" these latter, it need 

 hardly be stated, cannot recognise errors of a constant nature. The 

 table also includes a record of the barometer, and of the thermometers, 

 wet and dry in shade, and of black bulb in sun, together with an 

 exact statement as to the wind and aspect of sky. In all, the 

 observations at Mussooree include 392 in 0, and 361 in x ; those at 

 Dehra, 244 in and 217 in X, unavoidably excluding at the latter 

 station several taken on the first four days, because they were beyond 



* By means of the table of expansion for alcohol by Kopp given in " Gmelin's 

 Chemistry." 



N 2 



