90 Observations on the Glazing of Hot-houses. 



lap, being a thin piece of copper laid between the lap of the 

 panes, and turned downwards over the upper edge of the 

 lower, and upwards over the lower edge of the upper pane. 

 The copper lap is only applicable to glazing done in straight 

 lines, so that it cannot be used with the circular glazing : it 

 completely excludes the external air and wet from the inside 

 of the house, but retains the condensed steam within it, and 

 it effectually preserves the glass from breakage by frost ; but 

 where it is used, it is very difficult to replace the panes which 

 are accidentally broken. The piece of copper certainly 

 answers all the purposes of putty, but as it extends wider 

 than the putty would do in the same lap, the obstruction to 

 the light, by such a quantity of opaque matter in each sash, 

 is a great injury to the plants within the house : indeed, this 

 circumstance alone, if no other objection to them existed, 

 would be a reason for endeavouring to get rid of the wide 

 laps of glass, for dirt speedily collects in them when they are 

 not puttied, so far shutting out the light from the inside of 

 the house ; and since it is essential to the welfare of the plants 

 to receive as much of the influence of the sun's rays as pos- 

 sible, every diminution of such supply is injurious. 



Mr. Loudon has used, with apparent success, instead of 

 copper, sheet lead, rolled as thin as common drawing paper, 

 in the laps. This may be introduced, with or without putty, 

 with panes of any shape, and where it is used, the spaces for 

 the escape of the condensed steam may be left in the Circu- 

 lar, Rhomboidal, or Shield Glazing. It is not found neces- 

 sary to carry the lead over the upper or under surfaces of 

 the panes, but only to turn it upon the under edge or thick- 

 ness of the upper pane, and down on the upper edge of the 



