The field of cryptography will perhaps be the most rewarding.
密码技术也许是最实用的，可能也是最有回报的。
There is a remarkably close parallel between the problems of the physicist and those of the cryptographer.
这个问题对于物理学家来说，与对于密码学家来说，有很多一致之处，但也有所不同。
The system on which a message is enciphered corresponds to the laws of the universe, the intercepted messages to the evidence available, the keys for a day or a message to important constants which have to be determined.
对一条信息进行加密的过程，显然是遵循物理定律的，被拦截的信息会提供线索，而密钥则与日期或某些常数有关。
The correspondence is very close, but the subject matter of cryptography is very easily dealt with by discrete machinery, physics not so easily.
在这一点上是很有关系的，但用这种方法处理起来，却非常之困难，相比之下，如果采用离散机器来处理，则要容易得多。
There was more to Intelligent Machinery than this.
对于智能机器，这还没有说完。
One feature was that he laid down definitions of what was meant by 'machine', in such a way that it connected the 1936 Turing machine with the real world.
图灵还为"机器"做了一系列定义，这样就把1936年的图灵机与现实联系了起来。
He distinguished first:
他首先区别出：
'Discrete and 'Continuous' machinery.
"离散"机器和"连续"机器。
We may call a machine 'discrete' when it is natural to describe its possible states as a discrete set.
我们称一台机器是"离散的"，当它所有的状态可以被自然地描述为一个离散的集合
...The states of 'continuous' machinery on the other hand form a continuous manifold.
……而"连续"机器的状态则是无穷而连续的
...All machinery can be regarded as continuous, but when it is possible to regard it as discrete it is usually best to do so.
……微观来看，所有的机器都是连续的，但是只要有可能将其视为离散的，我们就应当尽量把它视为离散的。