“There cannot be mental atrophy in any person who continues to observe, to remember what he observes, and to seek answers for his unceasing hows and whys about things.”
Statement to a reporter a few months before he died, as quoted at Alexander Graham Bell Family Papers at the Library of Congress http://memory.loc.gov/ammem/bellhtml/bellinvent.html
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Alexander Graham Bell 20
scientist and inventor known for his work on the telephone 1847–1922Related quotes

“See a person's means (of getting things). Observe his motives. Examine that in which he rests.”
See a person's “being”, observe his motive, notice his result. How can a person conceal his character? [by 朱冀平]
The Analects, Chapter I, Chapter II
Context: See a person's means (of getting things). Observe his motives. Examine that in which he rests. How can a person conceal his character?

sa brahmacārī nijadharmacārī svakarmacārī ca na cābhicārī ।
cārī satāṃ cetasi nāticārī sa cāpacārī sa na cāpacārī ॥
Śrībhārgavarāghavīyam

The Philosophy of Physical Science (1938)
Context: For the truth of the conclusions of physical science, observation is the supreme Court of Appeal. It does not follow that every item which we confidently accept as physical knowledge has actually been certified by the Court; our confidence is that it would be certified by the Court if it were submitted. But it does follow that every item of physical knowledge is of a form which might be submitted to the Court. It must be such that we can specify (although it may be impracticable to carry out) an observational procedure which would decide whether it is true or not. Clearly a statement cannot be tested by observation unless it is an assertion about the results of observation. Every item of physical knowledge must therefore be an assertion of what has been or would be the result of carrying out a specified observational procedure. <!-- p. 9

Letter to A.S. Suvorin (October 27, 1888)
Letters

Source: undated quotes, Tàpies, Werke auf Papier 1943 – 2003,' (2004), p. 25.

"The core of the teachings (1980) http://www.jkrishnamurti.org/about-krishnamurti/dissolution-speech.php
1980s