【问】 It is not that the action of the scales in the one case，and the balance in the other，differ inthe principles of their construction or manner of working;but the beam of one is set on aninfinitely finer axis than the other，and of course turns by the addition of a much smallerweight.

[原译]这并不是说一方面使用的秤，同另一方面使用的天平，在结构和工作方式的原理上有差别;但是安装天平横杆的那个轴，要比秤杆的轴精细得多，所以即使加上一个非常小的重量，天平的横杆也会转动。(《科技英语理解与翻译》.P.95)我认为，把上句中的but译为“但是”是很费解的。请分析。

【答】 大家知道，有时候it is that=it is because。例如：

If I find fault，it is that I want you to do better in future.

如果我指责你的缺点，那是因为我希望你将来做得更好些。

not that...but(that)则是肯定一个原因，否定另一个原因，或者肯定一个判断，否定另一个判断。一般可以译为“不是因为……而是因为”、“(并)不是……而是”。

1. He felt a bit worried，not that comrades were not working hard，but that they did notpay enough attention to safety.

他有些着急，倒不是因为同志们不努力工作，而是因为他们不够注意安全。

2. Not that I loved Caesar less，but that I loved Rome more.

并非我爱凯撒浅，而是我爱罗马深。

3. Not that I am unwilling to go with you，but that I am busy now.

并不是我不愿意跟你一起去，而是我现在很忙。

4. Not that I dislike the work，but that I am unequal to it.

并不是我讨厌这个工作，实在是力不胜任。

5. It was not that I actually remembered anything at all. But my father had described overand over again what we should see at every milestone after leaving the nearest town.

这倒不是因为我还记得家乡的什么情况，而是因为父亲曾三番五次地向我描述过离开邻近的镇子之后，在每块里程碑旁边应该看到的景物。

[试译]……并不是前者所使用的秤和后者所使用的天平，在结构原理或工作方式上有什么不同，而是安装天平横杆的轴比秤杆轴精细得多……