508 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1915. 



Eecently switchboard cables, electromagnet coils, switchboard 

 cords, and in general the instruments themselves have been so im- 

 proved that operation in the tropics is not materially more trouble- 

 some than in the Temperate Zones. These improvements, which are 

 largely in the nature of moisture-proofing standard equipment or the 

 production of corresponding moisture-proof types, have resulted 

 from careful studies made by engineers in the Tropics. 



A few years ago there were many complaints about apparatus 

 involving wood manufactured in the United States and Europe and 

 installed in tropical countries. These complaints covered the de- 

 struction of the wooden portions by so-called "white ants." So 

 numerous did these complaints become that it was clearly evident 

 that some substitute for untreated northern woods would have to 

 be obtained. Two alternatives presented themselves — one, the use 

 of tropical woods which experience had shown to be relatively free 

 from termite attack, and the other, some treatment of the ordinary 

 Temperate Zone woods generally employed by telephone and tele- 

 graph companies. While the careful studies which were instituted 

 and which involved subjecting samples to actual exposure to termite 

 attacks have not yet been completed, it is clear that either teak or 

 mahogany is a relatively safe wood to employ. In some cases, of 

 course, the value of the apparatus hardly justifies the expense of 

 these woods, and doubtless cheaper substitutes will ultimately be 

 forthcoming. 



While the so-called " lead bug " is not confined solely to the Tropics, 

 its ravages appear to be more widespread there than in Temperate 

 Zone countries, such as the United States. Thus far no very effec- 

 tive economical means has been found for preventing its destructive 

 action, particularly to lead cable sheaths. Numerous experiments 

 are under way at the present time, some of which it is hoped will 

 lead to an amelioration of this trouble. 



In the matter of metal finishes, much improvement has been made 

 during the last three or four years particularly where iron or steel 

 parts are involved. Where long life for the apparatus is required it 

 has been definitely proven that the utmost precautions are required 

 in finishing apparatus intended for installation in the Tropics. In 

 general thoroughly satisfactory protective finishes must involve the 

 use of a coating of some nonrusting or rust preventing metal on the 

 iron, either with or without an additional covering of japan or 

 lacquer. 



SUMMARY. 



Summarized briefly, the principal developments in the field of 

 intelligence transmission during the last four or five years have been 

 the introduction of high-speed and printing telegraph systems; im- 



