And first before first --> READ THE DATASHEET of the LM35.
ALL IS EXPLAIN page 7 (National Semiconductor edition).
You have to protect the LM35 from capacitive load.
National recommends a serial resistor of 2kohms .
With 50 m Cat 5 ethernet cable I found an optimum for R = 4.7 kohms.
Other solution see picture.
In my opinion it is the best because it is independent of the length of the cable.
LM35 Output impedance as a value near from 0 Ohms so the line have to be matched by 100 ohms.
Arduino input impedance is > 100kohms so the line have to be AC matched by 100ohms.
