No. 68. lakewood, ()., Nov. 17, 1903.

I would like to operate a wireless telegraph a distance of about eight miles. Will the apparatus des cribed in the June and July numbers of 1902 be sufficient? If not, what changes should be made?

Please explain the system of wireless telegraphy or telephony using the earth alone as a conductor, and refer me to a book on same.

A. J. H

Wireless telegraphy instruments capable of transmitting messages over a distance of eight miles would have to be much more elaborate and expensive than those described in the June and July numbers of this magazine. The coil would require to be much larger and giving an eight to ten inch fat spark being necessary. The relay would also have to be of very high resistance, about 1000 ohrns. Relative to telegraphy or telephony, by using the earth for transmitting the cnrrents; much more work as has been done in this line has not been very fully described in the technica papers, so that the methods used could be fully de termined. Information on this subject will be welcomed for insertion in this column.

No. 69. Dorchester, Mass, Nov. 30, 1903.

Please give me a receipt for invisible ink, to be made visible by means of some chemical solution ?

C. E. B

A thin solution of arrowroot, used with a stub pen on rough paper, is developed by placing in steam of a weak solution of iodine in water, heated in a dish upon a stove. It fades again upon drying, but may be revived several times in the same way.