32 Prof. J. Joly on Scientific 



After 2 minutes B gets the second distance signal and 

 tells A " Distance 4 miles." And the Officer on A sees 

 that this also points to danger, for the distance of approach, 

 as observed, obviously has an error of excess and may easily 

 represent the danger distance of - 8 mile. And in this way 

 he continues to compare the successive announcements of 

 distance with the readings he gets on his Predictor by setting 

 forward at each announcement the cursor on a the distance 

 which A travels in 2 minutes. 



All this time he has a clear mental picture of where B is. 

 He can point to her compass direction and say she is there 

 at such a distance. Finally B alters her course so as to pass 

 clear of A and lets A know what she has done. The danger 

 is over. 



It is not improbable that the future extension to large 

 numbers of vessels of the powers conferred by recent 

 improvements in submarine signalling will result in a con- 

 siderable amount of the signalling between vessels being 

 carried out by this means : in this way reducing the number 

 of wireless messages required. 



We shall now consider the use of the 3rd criterion — that 

 which seeks to foretell threatened collision by observation of 

 the constancy of bearing. This criterion does not involve a 

 knowledge of the courses and speeds of the vessels. 



The wireless goniometer — which in late years has been 

 much improved— is claimed to afford a means of finding the 

 direction whence a wireless message proceeds, with much 

 accuracy; and this even with the use of considerable wave- 

 lengths. It is difficult to discuss these claims or to pronounce 

 on how far they may extend to conditions of hurry, anxiety, 

 and bad weather. Readings to a single degree have been 

 claimed. The polar diagram of the energy transmitted by 

 the Bellini-Tosi Directive Transmitter shows that some 10 

 or 11 degrees from the maximum of 88 microvolts the reading- 

 may be still 86 microvolts. Taking the distribution of 

 intensity, when the system is used as receiver, to be similar, 

 it would appear that the loudness of the sounds must vary 

 but slowly near the maximum. The setting depends entirely 

 on the discrimination of the direction of loudest telephonic 

 sound. Most of us find difficulty in determining maxima 

 when the senses, either of hearing or sight, are appealed to 

 quantitatively and by consecutive impressions. 



There must apparently exist a similar bar to attaining 

 reliability of goniometric readings in the case of finding 

 bearings by submarine signals. And the fact that an altered 

 course must, in general, be held while the bearing is 



