They also employed him to circumvent the patents they didnt' own, specificly those owned by Cooke & Wheatstone. But after those competing patents expired in 1851 Highton went off to found a competitor to the Electric company. that's why we have non-compete clauses today. Free to make his own projects as of 1852, Henry too k an interest in sending telegraph signals over bodies of water. They called it trans-aqueous communication. And more here.
Edward published a book 'The Electric Telegraph: Its History and Progress,' based on their initial research. It outlined their experiments and summarized their results. It’s out of print and you can’t even find it at auction really, but Google was kind enough to scan and post for the world to read for free here. This is totally diferent than the book of the same title written by George BartlettPrescott eight years later.
They began by sinking bare wires in canals. They were attempting to measure the loss of power durring immersion. They wanted to first find the mathmatical law that governed the loss of current when no insulation was used. Ultimately the proved that telegraph signals couldn't be sent any signifigant distance without insulation. It seems intuitive now, but at some point sombody has to theorize, test measure and prove these things. More here.
At the time there wire insulation was primitive and often failed. Most wire was used bare. So what begat the question was when the Brits tried to use bare wire in very wet places, say India. India is very wet. and is criss crossed by canals and wetlands. so any wires must cross numerous water-ways. Dr. W.B. O'Shaughnessy, performed some experiments using iron rods and in some cases no metallic conductors at all. He succeeded in passing some signals, but found the enormous power consumption to be cost prohibitive. The Society of Arts gave him a medal for this.
The brothers Highton decided there were 3 methods to trans-aqueous communication. The first uses copper plates heavy gauge wire and a heavy consumption of voltage. The second uses more sensitive instuments that can discern what little signal is not lost to the water. the third is perfectly insulated wire. By 1973 wire insulation was much improved and much cheaper. this new insulation was a solution of vegetable tar and lead oxide. Henry, not sore at all wrote a letter to the times endorsing the improvement.