1886.] S. A. Hill — Solar Thermometer Observations at Allahabad. 319 



For this only two causes in the least degree likely to produce the ob- 

 served effect suggest themselves, changes in the quantity of water va- 

 pour in the air and changes in the thickness of the dust haze of the 

 dry months. 



Regarding the proportionate quantity of the latter in the several 

 months, I think the scale laid down in my paper on the Lucknow obser- 

 vations probably represents the truth more exactly than that assumed 

 in my former paper on the Allahabad results. This scale is : — 



Jan. Feb. March. April. May. June. Oct. Nov. Dec. 

 35 7 9 10 6012 



The pressure of vapour and the total pressure of the air (whicb 

 does not differ by more than one per cent, from the true pressure of the 

 dry air alone) are given in the next two tables. The figures for June 

 are for the first half of the month only, the clear days as a rule being 

 confined to this half. 



Table II. — Mean Pressures of Water Vapour. 



Year. 



Jan, 



Feb. 



Mar. 



Apl. 



May. 



June. 



Oct. 



Nov. 



Dec. 



Mean. 



1876 



1877 

 1878 

 1879 



1880 

 1881 

 1882 

 1883 

 1884 

 1885 



•312" 



•428 



•364 



•325 



•335 



•284 



•335 



•381 



•335 



•396 



•295'' 



•349 



•431 



•354 



•349 



•357 



•289 



•298 



•312 



•291 



•356" 



•450 



•392 



•356 



•417 



•431 



•300 



•343 



•315 



•352 



•330" 



•534 



•486 



•325 



•400 



•433 



•348 



•393 



•293 



•374 



•524" 



•592 



•630 



•461 



•650 



•642 



•469 



•496 



•433 



•474 



•700" 

 •775 

 •515 

 •568 



•789 

 •859 

 •783 

 •693 

 •608 

 •563 



•678" 



-642 



•648 



•704 



•605 



•612 



•635 



•568 



•663 



•616 



•447" 



•474 



•454 



•365 



•409 



•352 



•428 



•354 



•423 



•401 



•843" 



•424 

 •318 

 •306 

 •340 

 •260 

 •348 

 •287 

 •373 

 •386 



•443" 



•519 



•471 



•422 

 •477 

 •475 

 •437 

 •424 

 •417 

 •428 



Mean 



•350 



•332 



•371 



•392 



•540 



•685 



•637 



•411 



•343 



•451 



Table III. — Mean Barometric Pressure. 29 inches + 



Year. 



Jan. 



Feb. 



Mar. 



Apl. 



May. 



June. 



Oct. 



Nov. 



Dec. 



Mean. 



1876 



1877 

 1878 

 1879 

 1880 

 1881 

 1882 

 1883 

 1884 

 1885 



•681 

 •795 

 •771 

 •723 

 •679 

 •779 

 •751 

 •731 

 •770 

 •7«1 



•626 

 •736 



•704 

 •646 

 •652 

 •690 

 •652 

 •683 

 •669 



•541 



•585 

 •599 

 •554 

 •509 

 •598 

 •557 

 •553 

 •537 

 •584 



•389 

 •506 

 •478 

 •402 

 •390 

 •417 

 •416 

 •400 

 •435 

 •452 



•300 

 •369 

 •380 

 •274 

 •305 

 •326 

 •337 

 •268 

 •297 

 •416 



•199 

 •303 

 •205 

 •219 

 •134 

 •194 

 •129 

 •185 

 •241 

 •264 



•605 

 •601 

 •482 

 •546 

 •562 

 •519 

 •492 

 •599 

 •608 

 •558 



•670 

 •678 

 •615 

 •686 

 •727 

 •653 

 •689 

 •655 

 •706 

 •714 



•787 

 •733 

 •693 

 •717 

 •768 

 •743 

 •711 

 •797 

 •794 

 •715 



•533 

 •590 

 •570 

 •530 

 •525 

 •547 

 •526 

 •541 

 •562 

 •553 



Mean 



•736 



•672 



•562 



•430 



•327 



•207 



•557 



•679 



•749 



•547 



