Withy. — On Sanitation and Ventilation. 459 



Appendix. — At the request of Mr. Harding, I add a figure 

 (Plate LI., fig. 12) which shows how pencils of parallel sun's 

 rays, entering the raindrop at a, a, after refraction, three re- 

 flections, and refraction again, issue at b, b, at an inclination 

 of about 65° away from the original direction, and parallel to 

 one another. These rays would, under very favourable con- 

 ditions, be powerful enough to be visible, and would form a 

 third rainbow, concentric with the primary and secondary 

 bows, and at a distance outside the secondary bow about 

 twice as great as the distance of the secondary from the pri- 

 mary, as shown in fig. 13, Plate LI. The order of the colours 

 in this tertiary bow would be the same as in the primary, and 

 it would be broader and fainter than the secondary bow. 

 This is what I should expect to see from geometric con- 

 struction ; and I imagine that it was the tertiary bow so 

 formed which Mr. Harding observed and described in his 

 paper. * 



I am unable to grasp the idea suggested in Mr. T. B. 

 Harding's note that a rainbow could be projected on a clear 

 sky by the sun's rays diffracted in passing through a granulous 

 cloud. I do not see how the essential conditions for the for- 

 mation of the picture of a rainbow in the eye of an observer 

 looking at this clear sky could occur under such circumstances. 

 I imagine that rain was really falling there, although not 

 uoticeable by the observer. 



Apt. LXIV. — Sanitation and Ventilation as required in a 



Modern House. 



By Edward Withy. 



[Read before the Auckland Institute, 3rd October, 1892.] 



Plates XLVIII. and XLIX. 



In dealing with these important subjects, I wish at the out- 

 set to make it clear to the audience that I do not presume 

 to speak as an expert either in the designing or executing of 

 the works required. It may therefore rjrevenfc some mis- 

 apprehensions, and open the door to freer criticism from 

 amateurs like myself, if I state that, merely from a desire to 

 insure healthy conditions in several houses which have been 

 built or altered for my personal occupation, I have been for 

 some years a reader and inquirer in the regions to be explored. 



* See above, Art. LXII. 



