| Flag, semaphore, and electrical or heliographic Morse signalling were all susceptible to interception by the enemy and thus dependent on codes and ciphers. |
| These assist in determining the heliographic latitude and longitude of sunspots. |
| Three methods to determine the heliographic latitude and longitude of sunspot groups are described below. |
| The day following I received a heliographic message from these burghers, who were now on the other side of the line. |
| In one division a regular pioneer squadron has been formed for telegraphic and heliographic duty. |
| The 4-inch heliographic telescope at SAAO in Cape Town, erected in 1876, is used to view sunspots. |
